This chapter provides an overview of a worker participatory approach to improve the psychosocial work environment in workplaces in Japan, and a unique tool, the Mental Health Action Checklist for a Better Workplace Environment (MHACL), that has been developed to facilitate this approach. Two cases, one successful and one less successful, are introduced to illustrate the fact that a healthy employee participation rate is crucial for a successful program for improving psychosocial work environment. To ensure employee participation in such a program, several strategies are considered.