A dopa oxidase acnvity inhibitor, a melanin production inhibitor, a skin whitening agent or an external preparation for the skin, which contains, as an active ingredient, Peristrophe japonica, an organic solvent extract thereof, a compound represen ted by formula (I) or a salt of the compound. (In formula (I), R i and R2 each represents a hydroxyl group or an alkoxy group having 1-4 carbon atoms, or alternatively R i and R 2 combine together to form a methylenedioxy group R3 and R4 each represents a hydroxyl group or an alkoxy group having 1-4 carbon atoms, or alternatively R3 and R4 combine together to form a methylenedioxy groupR5 represents a hydrogen atom, a hydroxyl group, an alkoxy group having 1-5 carbon atoms, an acyl group having 1-4 carbon atoms or a sugar residue such a s (D-Apio-p-D-furanosyl)oxy and R6 and R7 each represents a hydrogen atom and Rs and R9 combine together to represent an oxygen atom, or alternatively R8 and R9 each represents a hydrogen atom and R6 and R7 combine together to represent an oxygen atom.)
