To maintain stability of feedback control as the convergence properties of a rotation speed against a wide load fluctuation is insured, in idle rotation speed control to perform feedback control of an ignition timing and an intake air amount so as to effect convergence to a target idle rotation speed.

Feedback control of an ignition timing and an intake air amount is performed by feedback control and feedback control of a suction air amount is effected by proportional operation and feedback control of an intake air amount is effected by integration operation. A feedback gain in proportional control of an intake air amount is switched depending upon whether an ignition timing is corrected to a delay angle and advance angle limit through proportional control of the ignition timing.