To high-precisely decide a correction value of a feed fuel amount, based on an air-fuel feedback correction value.

Feedback control of an air-fuel ratio by using oxygen sensors 27L and 27R is performed. Vaporized fuel from a fuel tank 31 is adsorbed by a canister 33, and by opening a pure valve 36, vaporizing fuel from a canister is fed to a surge tank 3 togetherwith air. A purge valve 36 has an opening controlled to a target purge amount. When an air-fuel ratio feedback correction value CFB is inverted between an increase and a decrease, fuel concentration of purge gas is learnt, based on an average value of a present corfection value CFB during present inversion and a preceding correction value CFB during preceding inversion. A fuel injection amount is reduced from fuel injection valves 12L and 12R by an amount equivalent to an amount of fuel contained in purge gas decided based on learnt fuel concentration.