Invention suppresses deterioration of emission if there is air-fuel ratio imbalance among cylinders. Apparatus (100) controlling an engine including first and second air-fuel ratio sensors respectively disposed on upstream and downstream of catalyst, has: first determining device determining first F/B controlled variable according to deviation between output value and target value of first air-fuel ratio sensor; second determining device determining second F/B controlled variable according to deviation between output value and target value of second air-fuel ratio sensor; controlling device controlling fuel injection amount based on first and second F/B controlled variables; detecting device detecting air-fuel ratio imbalance among cylinders; and correcting device correcting second F/B controlled variable in direction in which there is hardly change of fuel injection amount to lean air-fuel ratio side, according to output deviation between first and second air-fuel ratio sensors, if air-fuel ratio imbalance is detected.