Objectives: This study validated the Japanese version of O’Donovan et al.’s (2020) composite measure of psychological safety scale and examined the associations of psychological safety with mental health and job-related outcomes. Methods: Online surveys were administered twice to Japanese employees with teams of more than three members. Internal consistency and test-retest reliability was tested using Cronbach’s α and intra-class correlation coefficient (ICC). Structural validity was examined using confirmatory factor analysis (CFA) and exploratory factor analysis (EFA). Convergent validity was tested. Multiple linear regression analyses were conducted to examine the relationship between psychological safety and psychological distress, work engagement, job performance, and job satisfaction. Results: Two hundred healthcare workers and 200 non-healthcare workers were analyzed. The Cronbach’s alpha of the total score was 0.92 - 0.96 and ICC was 0.88 - 0.92. CFA demonstrated poor fit, and EFA yielded a two-factor structure, suggesting one factor combined with peers and team. The scale showed good convergent validity. The total score of the scale showed significant associations with all outcomes in adjusted model in all workers. Conclusions: The Japanese version of the measure of the psychological safety scale presented good reliability and validity. Psychological safety is important for employees’ mental health and performance.