PROBLEM TO BE SOLVED: To provide a circadian rhythm regulator rich in experience as a food, having a high safety, easily available and excellent in processability.SOLUTION: A circadian rhythm regulator uses oleacein as an active ingredient. The circadian rhythm regulator can adjust the expressing amounts of Per1 gene and Bmal1 gene to an opposite phase, and as a result, can tune the expression rhythms of the Per gene and Bmal gene to a normal phase.