In a control apparatus for an internal combustion engine, wherein a fuel injection quantity calculated by fuel-injection-quantity calculation means is corrected with a purge-air-concentration learnt value calculated by subjecting a purge air concentration to purge-air-concentration filtering, and wherein fuel in the corrected fuel injection quantity is injected from an injector; a filtering effect in the purge-air-concentration filtering is changed in the direction of enhancing exhaust gas purification, between in a case where the purge air concentration is thick and in a case where it is thin, whereby an air/fuel ratio which is introduced into the internal combustion engine is precisely controlled to a target air/fuel ratio so as to enhance the exhaust gas purification.