To quickly and accurately compensate transitional excess and deficiency in a fuel injection amount due to such as an estimation error of a predicted intake air amount and steady excess and deficiency in the fuel injection amount due to such as performance variation of an injector.

In this fuel injection amount control device, a basic fuel injection amount (finjb(k)) is found depending on a predicted cylinder intake air amount (klfwd) based on a predicted operation condition amount of the engine. Based on an actual operation condition amount of the engine, a real cylinder intake air amount (klcy(k-1)) is found, and the excess and deficiency in fuel due to an error between the predicted cylinder intake air amount and the real cylinder intake air amount is corrected with a feed-forward (FF) system correction amount (finjk(k)), to find a FF fuel injection amount (finjfwd(k)). Further, the feedback (FB) system correction amount (finjfb(k)) is found based on a detected air-fuel ratio (abyfs) and an air-fuel ratio of an air-fuel mixture defined by the FF fuel injection amount (finjfwd(k)), and the FF fuel injection amount is corrected with the feedback (FB) system correction amount, thereby finding a final fuel injection amount (finjfinal(k)).