This study aimed to examine the reliability and validity of the Japanese version of the Chronic Pain Acceptance Questionnaire (CPAQ-8J). A total of 108 outpatients with chronic pain completed the CPAQ-8 questionnaire, along with the Acceptance and Action Questionnaire-II, Hospital Anxiety and Depression Scale, Pain Disability Assessment Scale, Numerical Rating Scale, and EuroQol 5 dimensions 5-level. Confirmatory factor analyses examined the factor structure. Results indicated that the CPAQ-8J comprised a two-component factor structure. Correlations between the CPAQ-8J and each variable were as expected, except between the “pain willingness” subscale and other scales ; thus, the CPAQ-8J had a certain degree of convergent validity. Internal consistency and test-retest reliability suggest that the CPAQ-8J is reliable. The psychometric properties of the CPAQ-8J meet a certain standard ; meanwhile, some issues must be addressed for its practical application. Further research should consider the influence of cultural characteristics in practical application. J. Med. Invest. 70 : 88-93, February, 2023