PURPOSE: To contrive to decrease the number of component parts as well as to make the device small by a method wherein the induction of auxuliary air for promoting the warming up of an engine at cold climate and the induction of auxiliary air for controlling idle speed of the engine are controlled by a single device.

CONSTITUTION: An auxiliary air inducing device 17 is equipped with a housing 19, which is interposed in the midway of an auxiliary air inducing passage 18 mounted around a throttle valve 2. A controlling valve 25, which seats to a valve seat 24 provided at the air outlet 20 of the housing 19 and are housed, through a spring 28, in the cylindrical part 27 of an operating rod 26 connecting to a diaphragm 32, is provided within the housing 19. A negative pressure chamber 33 is composed of a diaphragm 32 and a housing 19, and into said chamber 33, a suction negative pressure of an approximately constant valve is induced, through a constant pressure valve 38 being provided with a solenoid 39 which regulates the operating negative pressure. The solenoid valve 39 is controlled by a controlling device 43 so as to maintain the idling revolution speed at the predetermined value.