Disclosed is a compound which has an inhibitory activity on plasminogen activator inhibitor-1 (PAI-1) and has a propanedioic acid structure represented by formula (1) [wherein R1 and R2 independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms； R3 represents a cyclohexyl group or a phenyl group (provide that the phenyl group may be substituted by a substituent selected from a linear or branched alkyl group having 1 to 4 carbon atoms, a linear or branched alkoxy group having 1 to 4 carbon atoms, and a halogen atom)； R4 represents a linear or branched alkyl group having 1 to 6 carbon atoms or a phenyl group (provide that the phenyl group may be substituted by a substituent selected from a linear or branched alkyl group having 1 to 4 carbon atoms, a linear or branched alkoxy group having 1 to 4 carbon atoms, and a halogen atom)； and n represents an integer of 1 to 8.. The compound is useful as a prophylactic or therapeutic agent for pulmonary fibrosis.
