Provided is a clock gene expression level modifier having extensive history of use as a food, high safety, ready availability, and exceptional processability. A clock gene expression level modifier having as an active ingredient one or more compounds selected from the group comprising oleuropein, 3,4-DHPEA-EA, derivatives thereof, and salts thereof. The clock gene expression level modifier of the present invention makes it possible to adjust the expression levels of the Per1 gene and Bmal1 gene to the opposite phase and thereby tune the expression rhythm of the Per genes and Bmal genes to the normal phase.本發明係提供一種具豐富的食用經驗且安全性高，容易取得並具優異加工性之時鐘基因的表現量調整劑。本發明之時鐘基因的表現量調整劑，係以選自橄欖苦苷、3,4-DHPEA-EA、及該等之衍生物、及該等之鹽類所成群之一種以上的化合物為有效成分。本發明之時鐘基因的表現量調整劑，係逆向地調節Per1基因以及Bmal1基因的表現量，藉此可使Per基因以及Bmal基因的表現節奏同調為正常的方向。
