A control apparatus for an internal combustion engine, where a calculated fuel injection quantity is corrected with a purge-air-concentration learnt value calculated by subjecting a purge air concentration to purge-air-concentration filtering. A filtering effect in the purge-air-concentration filtering is changed in the direction of enhancing exhaust gas purification, when the purge air concentration is thick and when the purge air concentration is thin, whereby an air/fuel ratio introduced into the internal combustion engine is precisely controlled to a target air/fuel ratio so as to enhance the exhaust gas purification.