PURPOSE: To aim at simplification of constitution, by controlling ignition timing so that real engine speed may coincide with target engine speed at idling, and controlling air-fuel ratio according to the ignition timing.

CONSTITUTION: Whether or not an engine is at idling is determined by steps P1 and P3. If the engine is at idling, ignition timing is controlled by step P5 so that real engine speed may coincide with target engine speed. Then, fuel injection quantity is computed. Whether or not the engine is at idling is determined by steps P32 and P34. If the engine is at idling, and supply of fuel is not cut off, injection quantity is compensated by step P37 with use of compensated quantity of the ignition timing.