PURPOSE: To prevent occurrence of knocking without causing the feeling of deceleration, by attaching a combustion pressure sensor to each cylinder of an internal combution engine, and controlling the amount of exhaust gas to be recirculated to each cylinder through detection of knocking at each of the cylinders.

CONSTITUTION: Output signals of combustion pressure sensors 5, providd one for each of a plurality of cylinders of an internal combustion engine 1, are afforded via an amplifier 8 having a high input impedance to a band-pass filter 9 for taking out knocking signals in the frequency band of 6W10kHz produced when knocking is caused. A control circuit 10, which is furnished with output signals of the band-pass filter 9 and a crank angle detector 3, calculates the optimum amount of exhaust gas to be recirculated from the quantity of intake air and the engine speed together with the output signals of the band-pass filter 9 and the crank angle detector 3, taking it into consideration whether a knocking signal or signals are produced or not, and controls opening and closing of exhaust-gas recirculation valves 6 provided one for each cylinder in synchronism with the crank angle signal.