PURPOSE: To adequately maintain the engine torque, emission, fuel consumption, etc. by suppressing the knocking by the ignition timing control or the air fuel ratio control in response to the combustion state.

CONSTITUTION: A knocking detecting means is constituted of a combustion pressure sensor 6, a high-pass filter 9, an amplifier 11, and an amplification value detecting circuit 13. A combustion state detecting means is constituted of the combustion pressure sensor 6, a low-pass filter 10, an amplifier 12, and an amplification value detecting circuit 14. When the knocking occurs, a control unit 15 fed with outputs from them outputs the signal controlling the ignition timing in the knocking suppressing direction to an ignition unit 3 if the combustion state is good and outputs the signal controlling the air fuel ratio in the knocking suppressing direction to a fuel injection valve 5 if the combustion state is bad. Accordingly, the knocking is efficiently suppressed by the control of the ignition timing if the combustion state is good, and the knocking is suppressed by the control of the air fuel ratio while the torque loss is avoided if the combustion state is bad.