Disclosed are: a novel skin-whitening agent; and a skin-whitening cosmetic or quasi-drug which is highly effective for prevention/amelioration of melanopathy and is prepared using the skin-whitening agent. The cosmetic contains a compound represented by the general formula (I) and/or a salt thereof as an active ingredient. In the general formula (I), R1 and R2 independently represent a secondary or tertiary alkyl group having 3 to 7 carbon atoms; and R3 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to carbon atoms.