An agent for treatment and/or prevention of diabetic nephropathy, heart failure or the like, which contains a tricyclic compound represented by general formula (I) or a pharmaceutically acceptable salt thereof as an active ingredient. (In the formula, R1 represents an optionally substituted lower alkyl or the like； R2 and R3 may be the same or different and each represents a hydrogen atom or the like； R4 and R5 may be the same or different and each represents a hydrogen atom or the like； Q1-Q2-Q3 represents CH=CH-CH=CH or the like； Y represents a single bond or the like； Z1-Z2 represents C=CR13 (wherein R13 represents a hydrogen atom or the like)； and A represents a group selected from the group consisting of groups represented by formulae (b1)-(b6) (wherein R18 represents an optionally substituted lower alkyl or the like).)
