a few cycles in which knocking tends to occur easily makes it possible to control ignition timings so that correct control can be effected under the condition that the frequency of the occurrence of knocking is low on the whole the difference of this embodiment from the embodiment shown in fig5 resides in that the pickup 3b provided on the pulse rotor 1 and the waveshape shaping circuit 402 connected to the pickup 3b are removed and another circuit including a delay circuit 15 is provided between the shaping circuit 4 connected to the pickup 3 and the switching circuit 13 said delay circuit 15 delays the ignition pulse fed from the waveshape shaping circuit 4 by a predetermined period of time or a period of time corresponding to predetermined degrees of crankshaft angle and feeds same to the switching circuit 13 it is suitable to select the value of delay of said delay circuit 15 to correspond to the difference in ignition timing between the cylinder in which knocking tends to occur most easily and the cylinder in which knocking occurs most unlikely i e at least three degrees of crankshaft angle or more than that in accordance with the above the pulse rotor 1 is advanced in setting angle by said degrees of crankshaft angle to offset the value of delay made by the delay circuit 15 the arrangement as described above is one having.