Abnormality detection apparatus for electrically heated catalyst

An abnormality detection apparatus calculates an accomplishment ratio parameter based on an actually supplied electrical energy defined as the integrated value of electrical power actually supplied to the electrically heated catalyst over a specific period from the start of supply of electrical power to the electrically heated catalyst to a specific time and a target electrical energy defined as the integrated value of target electrical power over the specific period. The accomplishment ratio parameter is a parameter relating to the ratio of the actually supplied electrical energy to the target electrical energy. The abnormality detection apparatus detects an abnormality of the electrically heated catalyst on the basis of the accomplishment ratio. The specific time is a time after the start of supply of electrical power to the electrically heated catalyst and before or simultaneous with the time when the actually supplied electrical power substantially reaches the target electrical power.