PURPOSE: To detect knocks from any feeble knock to a large knock without the effect of revolution and load and without any misjudgment.
CONSTITUTION: The change rate of the heat occurrence, preferably, the maximum rise is operated based on the signal of a clank angle sensor 4 together with the signal of an in-cylinder pressure sensor 2, providing the in-cylinder pressure sensor 2 at the inwall of a combustion chamber 1. And, it is possible to change the quantity of delay angle of the ignition period, according to the difference between an operated value and a tolerable value, judging the knocking by the operated value, or to change the quantity of delay angle, taking not only the difference to the tolerable value but also the frequency over the tolerable value, depending upon the operation range.