An air-fuel ratio feedback system is configured to calculate the deviation between a target air-fuel ratio and an air-fuel ratio sensor value, multiplying a proportional gain by the calculated deviation to obtain a feedback correction value, and add the calculated feedback correction value to the in-cylinder injection quantity of an in-cylinder injector that is obtained by multiplying the fuel injection ratio of the in-cylinder injector by the basic fuel injection quantity. The calculated feedback correction value is not added to the port injection quantity of the intake manifold cylinder.