To prevent output reduction in an engine, a temperature rise in exhaust gas, and the deterioration in fuel consumption, by sufficiently restraining knocking even by a variable valve timing mechanism relatively slow in responsiveness, by quickly restraining the knocking, while minimizing the amount of timing delay of the ignition timing.

When the knocking is caused, an ignition timing delay value is set according to knock intensity, and the knocking is quickly restrained, by delaying the ignition timing by the amount of timing delay TRNK of integrating this ignition timing delay value. While the occurrence of the knocking continues, the amount of ignition timing delay TRNK is integrated/increased stepwise by the ignition timing delay value. When time exceeding a threshold value AR soon reaches preset time A, the valve timing is delayed, and the actual compression ratio of the engine is reduced, and the knocking is effectively restrained.