To reduce the parts weight of an actuator by detecting starting speed of current which flows in an electromagnetic coil when a rectangular voltage is imputted, and detecting the position of movable member from start speed of current which is detected thereby.

The current command value c of an air control valve is read in and memorized in S701, a table in which the staitonary state D of the current command value C is used is found out referably, and the inductance value D is memorized in s702. The starting characteristic of current which flows on an electromagnetic coil is detected as change caused when voltage of a shaft for detecting current is reduced, and a real inductance E is found out and memorized from an inclining in S703. The stationary state inductance D and the real inductance E are compared with each other in S704, it is judged that an air control valve is locked at an opening large in the case where the real inductance E is smaller than the stationary state inductance D, for example, reduction of fuel is made and an ignition timing is delayed, and thereby, real rotational speed is controlled to approach a target rotational speed.