[Object] The main obj ect of the present invention is to provide a fibrosis inhibitor. [Solving Means] 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), R 1 and R 2 are the same or different and each represents an optionally substituted aryl； R 3 and R 4 are the same or different and each represents hydrogen atom or alkyl； R 5 represents hydrogen atom, alkyl or halogen atom； Y represents N or N†’O； A represents NR 6 , and R 6 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.
