The aminopeptidase N inhibitor composition according to claim 1, which comprises an N-phenyl imide compound represented by the general formula (I?????????1): wherein each of R1 and R2 is a hydrogen atom, a lower alkyl group, a lower alkoxy group or a lower alkylthio group, Y is an oxygen atom or a sulfur atom, X1 is a halogen atom, a nitro group, a cyano group, a trifluoromethyl group, a hydroxyl