Background: The Emotion Regulation Skills Questionnaire (ERSQ) comprehensively assesses nine aspects of emotion regulation skills: awareness, clarity, sensation, understanding, compassionate self-support, modification, acceptance, tolerance, and readiness to confront. However, it is unknown about the levels of emotion regulation skills in various mental disorders, and its cross-cultural validity. We developed a Japanese version of the ERSQ, then examined its validity and reliability in clinical and non-clinical populations. Methods: In an Internet-based survey, 2684 participants (406 with MDD, 198 with PD, 116 with SAD, 66 with OCD, 636 with comorbid MDD and >= 1 anxiety disorder, and 99 with comorbid anxiety disorders; 1163 non clinical sample) answered the ERSQ, diagnostic status, and measures of mindfulness, emotion regulation, behavioral activation, psychological distress, and life satisfaction. Results: Confirmatory factor analysis (CFA) replicated the theoretical nine-factor structure of the original ERSQ. Higher-order factor analysis model assuming two second-order factors and nine first-order factors also showed adequate fit to the data, suggesting the factorial validity of the scale. Analyses of multi-group CFA indicated the equivalence of factor loadings across clinical and non-clinical subsamples. The levels of internal consistency and time stability were sufficient. Convergent validity of the scale was also confirmed for most of external criteria. Character on the emotion regulation skills for each diagnostic group was depicted. Limitations: Internet survey of samples with limited disorders, with self-reported diagnoses, may limit generalizability. Conclusions: The Japanese version of the ERSQ showed adequate reliability and validity.