PROBLEM TO BE SOLVED : To provide useful means for brown fat cell differentiation induction and thus contribute to the establishment of a new obesity prevention/treatment method.SOLUTION : The present invention provides a brown fat cell differentiation-inducing agent comprising a prenyl cinnamic acid derivative as an active ingredient. In a preferable embodiment, a prenyl cinnamic acid derivative and curcumin or a curcumin derivative are used in combination.SELECTED DRAWING : None