Disclosed are a method of preparation and method of application of a circadian rhythm regulatory agent having as an active ingredient an alkylresorcinol represented by general formula (I) below and a circadian rhythm regulatory agent containing as an active ingredient an alkylresorcinol-containing extract from a cereal or a nut containing an alkylresorcinol of the following general formula (I). In the following general formula (I), R1 is a saturated or unsaturated alkyl group and R2 is hydrogen or methyl. In general formula (I), R1 is preferably at the para-position with respect to R2, and R1 is preferably a saturated or unsaturated alkyl group having 15 to 27 carbon atoms. [Chem. 1]
