An object of the present invention is to clarify unelucidated aspects in the control mechanism of circadian rhythms. The present inventors have newly found that ROR.alpha. (retinoic acid binding-receptor alpha; the same shall apply hereinafter) stimulates an induction of Bmal1 expression and also that the induction of Bmal1 expression is promoted under hypoxia. These findings strongly suggest the existence of a control mechanism of circadian rhythms that, when ROR.alpha. expression is promoted under hypoxia or the like, an induction of Bmal1 expression is stimulated and, when the induction of Bmal1 expression is stimulated, binding between BMAL1 and CLOCK is stimulated and an induction of Per gene or Cry gene expression is stimulated. The present invention, therefore, has applicability as jet-lag regulating agents and anticancer agents.