To solve a problem wherein an intake valve amount sensor and an intake valve lift amount controlling mechanism require to be accurate, and system cost is increased when ISC required air quantity is intended to be materialized only by the intake valve having a wide air flow control range, to roughly control the ISC air quantity by the intake valve lift amount having the wide air flow rate control range, to adjust the air quantity beyond the range of the rough control according to a phase of the intake valve, and to materialize required flow rate with high accuracy.

The ISC air quantity is roughly controlled on the basis of the intake valve lift amount having the wide air flow rate control range (controlled by an integral multiple of air flow rate control minimum resolution). The air quantity beyond the range of the rough control is adjusted according to the phase of the intake valve. The phase of the intake valve control air quantity with about 0.4 to 1.2 times width to representation air quantity at that time, so that the air quantity is accurately controlled to be target air flow rate, and stable ISC target number of rotations is provided.