PURPOSE: To reduce minimum motion voltage of a solenoid valve by mounting a screw for adjusting cross sectional area of a passage in a passage in which an atmospheric chamber and a negative pressure chamber are mounted in a ISC valve provided with the atmospheric chamber and the negative pressure chamber communicated with a throttle valve and provided with the solenoid valve for switching the other passage between the both chambers.

CONSTITUTION: In an idle speed control valve provided with an atmospheric chamber 7 communicated with throttle valve upstream side of an intake system of an engine and a negative pressure chamber 8 communicated with downstream side and provided with solenoid valves 19, 19A for switching passages 10, 11 between the chambers 7 and 8, plungers 13 and 14 are arranged in such a manner that intake negative pressure applied to the same applies to a direction for closing the valves 19 and 19A. A passage 12 different from the passages 10 and 11 is mounted between the both chambers 7 and 8 and cross sectional area of this passage 12 is adjusted by a screw 15. Valve bodies 20 and 20A are fit in tip of the plungers 13 and 14 arranged at the atmospheric chamber 7 side and the solenoid valves 19 and 19A are opened by force against springs 22 and 22A of electromagnetic coils 23 and 23A.