Reality monitoring has been considered as a cause of a check compulsion, which is one dominantsymptom in obsessive-compulsive disorder (OCD). However, the previous studies could not confirm confusionsof reality monitoring in OCD checkers but found decrements of the confidence for memorizing (McNally& Kohlbeck, 1993; Constant, For, Franklin & Mathes, 1995). Since the previous studies had many problemsconcerning to the task and the hedonic value of stimuli, they could not discuss confusions of reality monitoringof OCD checkers sufficiently. The present study aimed to examine the reality monitoring of OCD checkers byusing an incidental learning task, which hedonic values of stimuli were experimentally controlled (neutral,negative and positive). As results, confusions of the reality monitoring of OCD were found in false alarms ofneutral and positive words. However, any decrement of the confidence for memorizing was not found. Theseresults were inconsistent with the finding of the previous studies.