<;P>;PROBLEM TO BE SOLVED: To provide a method for treating circadian rhythm failure by regulating circadian rhythm cycle, and to provide a fundamental therapeutic method of a disease caused by the circadian rhythm failure. <;P>;SOLUTION: The circadian rhythm failure-ameliorating agent contains lycorins or lycoricidinols of alkaloids of Amaryllidaceae family, or a pharmacologically acceptable salts thereof as an active ingredient. The medicinal composition for the prevention or therapy of the disease caused by the circadian rhythm failure is also provided. <;P>;COPYRIGHT: (C)2011,JPO&INPIT