To provide a substance capable of safely and effectively modulating expression of a period gene. An expression modulator for a period gene containing Pelargonium plant extract as an effective component.本發明之課題在於提供一種可安全且有效地調節Period基因表現之物質。本發明係一種Period基因表現調節劑,其含有天竺葵屬植物之萃取物作為有效成分。