PURPOSE: To improve the accuracy in deciding the knocking intensity of each cylinder by constituting a titled device in such a way that the knocking intensity is decided from the ratio between the representative output value of the cylinder obtd. by each pressure sensor in the cylinder provided to each cylinder and the representative output value of knocking components.

CONSTITUTION: Pressure sensors 13 in cylinders mounted in respective cylinders are designated as 13A, 13B, 13C and 13D, and when the cylinders are ignited in this order, the outputs proportional to the pressure in the cylinders are successively outputted from the sensors 13AW13D of the respective cylinders to a knocking circuit 100. A 1° detection signal 16 and a 720° detection signal 17 are supplied at the same instant from a crank angle sensor 15 provided internally in a distributor 11 to the circuit 100. The circuit 100 is so constituted that the ratio N1/PD value between the representative value N1 of the knocking component in each cylinder and the representative ouput value PD is obtd. Said value is stored as the value indicating the knocking intensity in an RAM. When the value is larger than a prescribed value, it is judged as knocking and the knocking intensity by each cylinder is exactly decided.