PURPOSE: To avoid knocking by detecting the acceleration state based on the throttle valve opening or the change quantity of the throttle valve opening and delayingly correcting the ignition timing if the detected acceleration state is in the decreasing direction of the engine rotating speed.

CONSTITUTION: A control unit 22 receives detection signals of a crank angle sensor 20, a throttle sensor 30, a pressure sensor 28, etc. and determines the ignition timing with correction for the water temperature or the like. Next, when an engine is in an acceleration state and the engine rotating speed change rate is the preset decreasing rate or higher, a preset value is subtracted from the acceleration correction value, and the ignition timing is delayingly corrected. When the change rate is the preset decreasing rate or lower and subsequently becomes the preset increasing rate or higher on the contrary, a fixed value is added to the acceleration correction value, and the ignition timing is advanced. When the change rate is the preset increasing rate or lower, reduction in lead is not carried out. When acceleration is not detected, the ignition timing is not delayingly corrected. This calculation is performed for every 30° of the crank shaft rotation angle, the ignition timing is corrected, the final ignition timing is determined, and a time-converted ignition timer is activated for ignition.