The causal effects of working time on mental health: The effectiveness of the law reform raising the overtime wage penalty

The present paper reexamines the causal effect of working hours on workers’ mental health. We utilize Japan's 2010 reform of the Labor Standards Act as a social experiment to examine how the increased wage penalty for long overtime work affects working hours and workers’ mental health. Utilizing a unique panel dataset containing health behaviours as well as individual, household and workplace characteristics of male workers, we find that the wage penalty reform indeed succeeded in reducing overtime hours and total working hours and that the reductions contributed to better mental health of workers. Further empirical investigation suggests that the reduction effect of the reform on working time is homogeneous among age groups; however, the harmful effect of working time on mental health is large and statistically significant among young workers. Our results suggest that setting a high wage penalty for long overtime work effectively reduces overtime work and improves workers’ health outcomes, particularly for young people.