The present invention provides a substance which can modulate expression of a Period gene effectively and with a wide range of application. Provided is an expression modulator for the Period gene comprising, as an active ingredient, one or more selected from the group consisting of arnica extract, nuphar extract, black tea extract, Zanthoxylum extract, juniper oil, cedar oil, lavender oil, clove bud oil, cypress oil, rose oil, ylang-ylang oil, galbanum oil, petitgrain oil, pepper oil, thyme oil, basil oil, and beta-caryophyllene.
