Purpose: Accurate evaluation of medication adherence is important; however, no simple evaluation scale that is applicable to patients with bipolar disorder has been established in Japan. In this study, we prepared a modified Japanese version of a self-rating scale for medication adherence in the field of psychiatry, the Brief Evaluation of Medication Influences and Beliefs (BEMIB), and investigated its reliability and validity. Methods: Forty-one patients with bipolar disorder who visited several facilities, including Nagoya University Results:The Cronbach α coefficient of the Japanese version of BEMIB was 0.73. Four-week test-retest reliability coefficients of each item and the BEMIB total score were 0.39-0.68 (p < 0.05) and the intra-class correlation coefficient was 0.63 (95% CI = 0.33-0.75, p < 0.001). In addition, a significant positive correlation was observed between the BEMIB and DAI-10 total scores (Pearson's correlation coefficient = 0.39, p < 0.001), showing that the concurrent validity was sufficient. Discussion: The Japanese version of BEMIB modified for patients with bipolar disorder is sufficiently reliable and valid. We suggest that this simple evaluation scale of medication adherence in patients with bipolar disorder is applicable in routine medical practice.