The present invention relates to a benzazepinone compound represented by the following formula (I): wherein R 1 represents a C 1 -C 6 alkyl group or halogeno C 1 -C 6 alkyl group, R 2 represents a carboxyl group which may be protected, and Y represents a group represented by the formula (II): wherein Z represents CH or a nitrogen atom, or a pharmaceutically acceptable salt thereof.