An idle speed control device has an electromagnetic driving portion and a flow rate controlling portion disposed in a bypass passage formed in a throttle chamber such as to bypass a throttle valve. The flow rate controlling portion has a body defining a passage for the fluid to be controlled, a seal formed in an intermediate portion of the passage, a first valve driven by the plunger of the electromagnetic driving portion through a rod such as to be brought into and out of contact with the seat, a sleeve disposed in the body, and a second valve connected through a rod to the downstream side of the first valve such as to produce a vacuum force which acts in the opposite direction to the vacuum force produced on the first valve thereby to absorb any fluctuation in the intake pressure in cooperation with the first valve, the second valve being loosely received by the sleeve. According to this arrangement, it is possible to eliminate any unfavorable effect of the fluctuation in the intake vacuum on the actual air flow rate. In addition, since the flow from the vacuum compensating portion is minimized, the vacuum compensation is made possible without incurring any increase in the initial leak.