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.