The main object of the present invention is to provide a fibrosis inhibitor. The present invention relates to a fibrosis inhibitor containing the heterocyclic derivative represented by the following general formula (1) or a pharmaceutically acceptable salt thereof as an active ingredient:In the formula (1), R1 and R2 are the same or different and each represents an optionally substituted aryl； R3 and R4 are the same or different and each represents hydrogen atom or alkyl； R5 represents hydrogen atom, alkyl or halogen atom； Y represents N or N→O； A represents NR6, and R6 represents hydrogen atom, alkyl, etc.； D represents alkylene or alkenylene which is optionally substituted with hydroxy； E represents phenylene or a single bond； G represents O, S, etc.； and Q represents carboxy, alkoxycarbonyl, etc.
