In assessing the endorsement of conspiracy theories, researchers often employ a general approach by measuring adherence to abstract statements rather than specific, concrete conspiracies. One commonly used measure is the Conspiratorial Mentality Questionnaire (CMQ, Bruder et al., 2013). The present study aimed to develop a Japanese version of the CMQ (CMQ-J) and examine its factor structure, construct validity, and test-retest reliability. The results of this study revealed that the CMQ-J demonstrated high internal consistency and temporal stability. It also exhibited positive correlations with existing measures of conspiracy theory, as well as authoritarianism and paranoia, while showing a negative correlation with trust in institutions. These findings indicate that the CMQ-J is a reliable and valuable tool for assessing general inclinations towards conspiracy theories. However, the factor structure of the scale differed from the original version, suggesting a need for future research.
