To provide a fuel controller of an engine capable of accurately controlling fuel injection by accurately detecting intake air amount in the full operation range of the engine.

This fuel controller comprises an air flow sensor 8 detecting the flow Qa of the air in the intake passage 3 of the engine 1, a manifold pressure sensor 68 detecting a pressure in the intake passage 3, and an air-fuel ratio sensor 65 detecting an air-fuel ratio in the exhaust gases from the engine 1. When the engine reaches a predetermined low intake air amount range E1 while the engine is operated in an air-fuel ratio feedback control range, the control of the fuel injection amount based on the intake air amount Qa2 calculated from the detected value of the air flow sensor 8 is switched to the control of the fuel injection amount based on the intake air amount Qa1 calculated from an intake pipe pressure Pi before injection control.