PURPOSE: To prevent the dielectric breakdown of the insulator of an ignition plug, by controlling the igniting condition of plural ignition plugs so that the demand voltage of the ignition plugs on the delayed ignition side becomes lower than an allowable voltage, thereby the condition of combustion in a cylinder is controlled.

CONSTITUTION: An engine E is provided with two of first and second ignition devices 20, 40 which have first and second ignition coils 21, 41, respectively. The ignition timing of the device 40 is delayed from that of the device 20, and therefore, the rising of demand voltage of a ignition plug 43 of the device 40 is assisted. When the demand voltage value of the ignition plug 43 exceeds an allowable voltage value, a comparator circuit 48 delivers a spark advance compensating signal S6 to a spark advance compensating circuit 47 that therefore delivers an adjusted ignition signal S'21 by which the spark advance is shifted from the optimum spark advance, and therefore, the ignition plug 43 is energized upon low cylinder pressure so that the output of an engine declines. Howeer, the demand voltage value of the ignition plug 43 is lowered to protect its insulator.