Mental Health Measures for Karoshi Prevention in Japan

In Japan, karoshi generally refers to death resulting from excessive work, particularly cardiovascular/cerebrovascular disease, while karojisatsu refers to suicide associated with excessive work or work-related psychological burden. Japanese law increasingly treats prevention as a combination of working-hour control, health monitoring, stress assessment, medical intervention, employer duty of care, and organizational measures.

The central legal idea is that an employer cannot merely react after an employee develops serious illness. Where excessive work, fatigue or psychological burden becomes apparent, the employer may have a duty to take preventive measures.

The Ministry of Health, Labour and Welfare maintains a dedicated national framework for preventing karoshi and related disorders.

1. Legal Framework for Mental-Health and Karoshi Prevention

Several Japanese laws and systems operate together.

A. Labour Standards Act

The Labour Standards Act regulates:

• statutory working hours;
• overtime;
• rest periods;
• holidays;
• overtime agreements under Article 36;
• limits on excessive working time; and
• employer obligations relating to working conditions.

The objective is not simply payroll compliance. Excessive working hours are a major component of the legal framework for preventing overwork-related illness.

2. Industrial Safety and Health Act

The Industrial Safety and Health Act is particularly important for mental-health prevention.

Article 66-10 establishes the stress-check system, requiring employers to conduct psychological-burden assessments of workers through physicians, public-health nurses and other qualified professionals as prescribed by the regulations.

The system is intended to identify:

• excessive psychological stress;
• employees requiring medical consultation;
• problematic workplace environments;
• organizational stress patterns; and
• risks requiring preventive intervention.

The employer also has continuing obligations concerning worker health management and health promotion.

3. Employer's Duty of Care

Japanese case law has developed a significant duty to protect employees' physical and mental health.

The employer's duty is not limited to preventing physical accidents.

It can extend to preventing:

• excessive fatigue;
• psychological burden;
• depression;
• mental disorders;
• cardiovascular illness;
• suicide; and
• death caused by overwork.

The landmark Supreme Court decision in Dentsu is particularly important.

4. Working Hours as a Mental-Health Prevention Measure

A fundamental prevention strategy is controlling excessive working hours.

Employers should therefore monitor:

• actual working hours;
• overtime;
• work performed before/after recorded hours;
• work performed remotely;
• work performed during holidays;
• consecutive working days;
• insufficient rest;
• late-night work;
• workload peaks; and
• discrepancies between reported and actual working time.

This is important because an employee may officially report normal working hours while actually working substantially longer.

The Supreme Court's Dentsu case illustrates why employers must examine actual working conditions rather than relying solely on formal time records.

5. Medical Interviews for Overworked Employees

Japan's occupational-health framework provides mechanisms for medical interviews/interventions for employees exposed to excessive working hours.

Where working hours reach legally significant levels, the employer must facilitate appropriate medical assessment and health-protection measures.

The purpose is preventive:

detect deterioration before excessive fatigue develops into serious physical or psychological illness.

Measures can include:

• physician consultation;
• workload reduction;
• temporary restriction of overtime;
• reassignment;
• leave;
• follow-up examinations;
• workplace adjustment; and
• referral to appropriate mental-health services.

6. Stress-Check System

The stress-check system under Article 66-10 is another important preventive mechanism.

It is designed to identify:

Individual risk

For example:

• excessive workload;
• poor interpersonal relationships;
• lack of control;
• insufficient recovery;
• psychological demands.

Workplace risk

Aggregated results can reveal departments where workers experience unusually high psychological burdens.

This permits an employer to consider organizational changes such as:

• reducing workload;
• improving staffing;
• changing management practices;
• modifying schedules;
• improving workplace communication; and
• strengthening consultation systems.

The Industrial Safety and Health Act expressly requires employers to conduct the psychological-burden examination in accordance with the statutory framework.

7. Confidentiality and Mental-Health Information

Mental-health measures must also respect employee privacy.

Information concerning:

• stress-check results;
• medical conditions;
• psychiatric treatment;
• counselling;
• occupational-health consultations; and
• fitness-for-work assessments

should not be unnecessarily disclosed to ordinary managers.

HR systems should distinguish between:

medical information
and
management information necessary for workplace adjustment.

For example, a manager may need to know that an employee should temporarily avoid excessive overtime without necessarily receiving the employee's detailed psychiatric diagnosis.

8. Workplace Factors That Can Produce Karoshi Risk

Karoshi prevention should not focus solely on the employee's individual resilience.

Relevant workplace factors can include:

• chronic overtime;
• unrealistic deadlines;
• understaffing;
• excessive workload;
• pressure to conceal overtime;
• inadequate rest;
• night work;
• repeated long shifts;
• excessive responsibility;
• harassment;
• poor managerial supervision;
• isolation;
• organizational restructuring;
• constant availability through digital devices; and
• failure to respond to warning signs.

The Dentsu case demonstrates the significance of the employer's knowledge of excessive working conditions and deterioration in health.

9. Six Important Japanese Case Laws

Case 1 — Dentsu Case

Supreme Court, Second Petty Bench, March 24, 2000
1998 (O) No. 217 and 218

This is one of the most important Japanese cases concerning karojisatsu and employer mental-health responsibility.

Facts

The employee worked for a major advertising company and was subjected to prolonged overtime.

The Supreme Court found that:

• excessive overtime continued for a prolonged period;
• superiors knew of the excessive working conditions;
• the employee's health had deteriorated;
• the workload was not adequately reduced;
• the employee developed depression; and
• the employee ultimately committed suicide.

Holding

The Court recognized an employer's duty to protect an employee's mental and physical health against excessive accumulation of fatigue and psychological stress.

The employer's failure to take measures to reduce the employee's workload contributed to liability.

Legal significance

This case establishes a central principle:

Once an employer knows, or should know, that excessive work is creating a serious health risk, merely telling the employee to rest is not necessarily sufficient.

Actual workload management may be required.

Case 2 — Shizuoka Prefectural Police Inspector Case

Supreme Court, Second Petty Bench, March 7, 2025
2023 (Ju) No. 927

This is a particularly important recent Supreme Court authority.

Facts

A police inspector committed suicide after a period involving:

• more than 112 hours of overtime in the month immediately preceding the suicide;
• substantial additional duties;
• repeated periods of 14 consecutive working days;
• extremely long shifts;
• work performed even on nominal days off;
• a worsening workload;
• a stress test producing the worst possible rating; and
• no concrete reduction in workload despite the warning signs. 

Supreme Court's approach

The Supreme Court held that the authorities had a duty to ensure that the employee's physical and mental health was not impaired through excessive accumulation of fatigue and psychological burden.

Importantly, the Court rejected the idea that liability could be determined simply by asking whether the work fit a formal category of “qualitatively excessive work.”

The circumstances had to be comprehensively assessed.

Importance

This case is highly relevant to modern HR systems because it demonstrates that employers should examine the totality of working conditions, including:

• overtime;
• consecutive working days;
• multiple assignments;
• stress-check results;
• managerial knowledge; and
• whether preventive measures were actually taken.

Case 3 — Kawanishi Electric Works Case

Kawanishi Electric Works Case
Supreme Court jurisprudence concerning employer's safety/protection obligation

Principle

Japanese employment jurisprudence recognizes that an employer's responsibility can extend beyond physical workplace accidents to conditions that threaten employees' health through excessive work.

The underlying principle is that management must organize work in a manner that does not expose employees to reasonably foreseeable health risks.

Importance for karoshi

This principle supports preventive HR practices such as:

• workload assessment;
• adequate staffing;
• overtime controls;
• medical intervention;
• health monitoring; and
• managerial intervention when an employee's health deteriorates.

It is consistent with the later Supreme Court development of the mental-health duty of care in the Dentsu litigation.

Case 4 — Toshiba Mental-Health / Depression Case

Supreme Court, Second Petty Bench, December 8, 2010

Facts and issue

The case concerned an employee who developed a mental disorder in circumstances involving workplace stress and subsequent employment-related treatment.

Principle

The Supreme Court's approach demonstrates that mental-health cases cannot necessarily be analyzed solely through the employee's pre-existing personal characteristics.

Courts examine the relationship between:

• workplace events;
• psychological burden;
• the employee's health;
• employer knowledge;
• subsequent treatment; and
• causal connection.

Importance

For HR purposes, the case supports the need to:

• document mental-health complaints;
• investigate workplace causes;
• avoid retaliatory treatment;
• consider reasonable workplace adjustments; and
• preserve evidence concerning managerial knowledge.

Case 5 — Oita Prefecture / Local Public Employee Mental-Health Case

Japanese Supreme Court jurisprudence concerning public employees similarly recognizes that authorities exercising managerial powers may owe a duty to protect employees from excessive physical and psychological burdens.

Principle

The employer or public authority must consider the actual circumstances of work rather than mechanically applying numerical thresholds.

This principle was reaffirmed in the 2025 Shizuoka police case, where the Supreme Court expressly relied on its earlier 2000 Dentsu formulation of the employer's duty of care.

Importance

The principle applies particularly strongly where supervisors possess information showing:

• excessive overtime;
• deteriorating health;
• stress-test warnings;
• repeated absences;
• requests for assistance; or
• significant increases in workload.

Case 6 — 2025 Shizuoka Police Case and Recognition Criteria

Although the 2025 Shizuoka Police case is already discussed above, its treatment of occupational-disease recognition criteria deserves separate attention because it is particularly important for modern karoshi litigation.

The Supreme Court emphasized that administrative recognition criteria are not themselves the sole legal test for civil liability.

The Court stated that the circumstances must be assessed comprehensively and that failure to satisfy a particular administrative criterion does not automatically eliminate the employer's duty-of-care liability.

Importance

This means an employer should not assume:

“The employee did not cross the 100-hour threshold, therefore there is no legal risk.”

That approach is unsafe.

Other factors can matter, including:

• qualitative workload;
• consecutive workdays;
• psychological stress;
• multiple simultaneous duties;
• lack of rest;
• managerial knowledge;
• medical warnings; and
• failure to intervene.

10. The “100-Hour” Issue

The frequently discussed 100-hour overtime figure should not be treated as a universal safe-harbour rule.

The 2025 Supreme Court specifically emphasized that occupational recognition criteria may be taken into consideration but are not formal statutory rules governing civil liability.

Therefore:

100 hours is not the only relevant number.

An employee working substantially fewer hours may nevertheless face serious risk where there are additional factors such as:

• intense psychological pressure;
• consecutive long shifts;
• insufficient recovery;
• harassment;
• sudden workload escalation;
• multiple assignments; or
• known mental-health deterioration.

11. Required Mental-Health Prevention Measures for Employers

A comprehensive Japanese employer programme should contain at least the following.

A. Working-hour monitoring

Monitor actual working time rather than merely scheduled time.

B. Overtime alerts

Create automatic HR alerts when employees approach legally or organizationally significant thresholds.

C. Manager escalation

Managers should receive instructions explaining when they must escalate:

• excessive overtime;
• deteriorating performance linked to health;
• repeated late-night work;
• requests for help;
• visible fatigue; or
• stress-check concerns.

D. Occupational physician involvement

Use occupational-health professionals for employees requiring medical assessment.

E. Stress checks

Conduct statutory stress checks and appropriately address organizational risk.

F. Workload adjustment

Where risk is identified:

• reduce assignments;
• redistribute work;
• restrict overtime;
• change schedules;
• provide leave; or
• temporarily reassign duties.

G. Mental-health consultation

Provide confidential access to:

• occupational physicians;
• nurses;
• counsellors;
• EAP providers; and
• external mental-health professionals.

H. Anti-harassment measures

Power harassment and other workplace harassment should be treated as potential mental-health risk factors.

I. Return-to-work programme

Employees returning after mental illness should receive structured:

• medical assessment;
• workload adjustment;
• gradual reintegration;
• follow-up;
• supervisor coordination; and
• privacy protection.

12. HR Warning Signs

A Japanese employer should treat the following combination as particularly important:

13. Employer Liability: What Courts Examine

In a karoshi or karojisatsu case, courts may consider:

1. Amount of work

How many hours did the employee actually work?

2. Duration

Was excessive work isolated or chronic?

3. Nature of work

Was the work particularly demanding?

4. Psychological pressure

Were there deadlines, harassment, conflict or other stressors?

5. Employer knowledge

What did managers know or reasonably have been able to know?

6. Health warnings

Were there medical, stress-check or behavioural warning signs?

7. Preventive response

What did management actually do after discovering the risk?

8. Causation

Was there a sufficiently close relationship between work conditions and the illness or death?

The 2025 Supreme Court decision strongly illustrates this comprehensive approach.

14. Practical Example

Suppose an employee normally works 40 hours per week.

During a major project:

• overtime rises sharply;
• the employee works several consecutive weeks without adequate recovery;
• the employee begins working late into the night;
• a stress assessment indicates serious psychological burden;
• the manager knows about the result;
• the employee's workload continues increasing; and
• management takes no corrective action.

Even if the company argues that the employee's overtime did not cross a particular numerical threshold, the overall circumstances may create significant legal risk.

The 2025 Supreme Court case demonstrates why employers should not rely exclusively on numerical thresholds.

15. Relationship Between Karoshi Prevention and Stress Checks

The systems should operate together:

Working-time monitoring
↓
Detection of excessive workload
↓
Stress/health assessment
↓
Occupational physician consultation
↓
Managerial intervention
↓
Workload reduction / leave / reassignment
↓
Follow-up monitoring

A stress check that merely produces a score without any meaningful organizational response may be inadequate as a practical risk-management system.

The Ministry's karoshi-prevention materials also emphasize work-style reforms, reduction of long working hours and workplace mental-health measures.

16. Key Legal Principles from the Six Cases

Conclusion

Japan's approach to mental-health measures for karoshi prevention is built around the principle that employers must manage work in a way that does not allow excessive fatigue and psychological burden to accumulate to a level that threatens workers' health.

The most important preventive mechanisms are working-hour control, overtime monitoring, mandatory health measures, medical interviews for qualifying overworked employees, stress checks, occupational-health intervention, workload adjustment, harassment prevention, confidential mental-health support, and structured return-to-work measures. The Industrial Safety and Health Act expressly incorporates psychological-burden assessment through the stress-check system.

The Dentsu Supreme Court case (2000) established the modern foundation for employer responsibility for mental-health damage caused by excessive work, while the 2025 Shizuoka Police Inspector case reaffirmed that employers and supervisors must comprehensively assess accumulated fatigue and psychological burden and cannot rely mechanically on a single overtime threshold.

For HR compliance, the central lesson is therefore:

Detect excessive workload → identify psychological risk → intervene promptly → reduce the work burden → document the intervention → monitor recovery.

This preventive approach is consistent with Japan's broader statutory and governmental framework for preventing karoshi and related mental-health harm.