PURPOSE: To suppress fluctuation of flow by executing duty control in such a manner that power conduction is finished upon reaching of the integrated value of current to a target value corresponding with a flow control value after starting power conduction to an electromagnetic coil with predetermined period.

CONSTITUTION: On the basis of the operating condition of engine, a microcomputer 18 will set a flow control value of an idle speed control valve and a corresponding target integrated value. Then on the basis of pulse signals from a timer 15 to be produced with predetermined period, a flip-flop 14 is set to bring the output into H-level thus to turn on a transistor 12 and to start conduction of power to an electromagnetic coil 11 to move the valve body in the opening direction. Thereafter, the current flowing through said coil 11 is accumulated on the basis of the terminal voltage of a resistor 16 for detecting the current and upon decision that the accumulated value has reached to a target value, the flip-flop 14 is reset to bring the output into L-level thus to turn off the transistor 12 and to finish power conduction to said coil 11.