In this study, the Japanese version of the Treatment Self-Adjustment Questionnaire for Diabetics (TSRQ-DJ), an instrument that asks people with type 2 diabetes their reasons for engaging in diabetic self-management behaviors, was developed and validated. A questionnaire survey was administered to a panel of patients with diabetes who registered with an online survey company, and 510 valid responses were obtained. A confirmatory factor analysis revealed that the model fit of the two-factor, 19-item structure, which was the same as the original version, was low; thus, the questionnaire was refined to a two-factor, 14-item structure. The goodness of fit of the improved model (GFI, 0.91; CFI, 0.6; and RMSEA, 0.08) indicated that the model fit was generally good. Cronbach's alpha was 0.91, indicating high reliability. The "autonomous motivation" and "controlled motivation" subscales showed a positive correlation (r_s = 0.49). J-SDSCA-r, PCDS, and each subscale showed a positive correlation, similarly to the characteristics of the original version of the TSRQ. In conclusion, the TSRQ-DJ is a reliable and valid scale, and its potential for use as a Japanese version of the TSRQ has been demonstrated.