Disclosed is a compound having a lactam skeleton or a salt thereof, which is useful as a PPAR activator. Specifically disclosed is a lactam compound represented by formula (1) or a salt thereof. (1) wherein R1 represents a halogen, a hydrocarbon group, a carboxyl group or the like； Z1 represents an arene ring or a hetero ring； Z3 represents an alicyclic or aromatic hydrocarbon ring； Z2 represents a 5- to 6-membered ring containing a nitrogen atom； X1 represents a C, O, S or N atom, a group -N-C(=O)- or a group -C(=O)-N-； R2 represents a hydrogen atom or an alkyl group which may have a substituent； R3 and R4 independently represents a single bond or a bivalent aliphatic hydrocarbon group, provided that at least one of R3 and R4 represents an aliphatic hydrocarbon group； X2 and X3 independently represent a single bond, an O or S atom, an imino group or the like； A1 represents a single bond or a phenylene group which may have a substituent； Y1 represents a hydrogen atom, a halogen atom, a carboxyl group or the like； a represents an integer of 0 to 5； b represents an integer of 0 to 2； and c represents an integer of 1 to 3.
