To reduce a number of part items and assembly man-hours and improve assembly accuracy, in an intake air amount control device controlling a throttle valve bypass air flow amount in an engine intake pipe line and setting an idling speed to a required speed.

A housing 6 of a control valve 5 and a throttle body 1 are formed into an integrally molded product, a number of part items and assembly man-hours are reduced, and a valve unit 9 rotated by an electric motor 20 and bearings 12, 13 supporting valve shafts 10, 11 in both ends of the valve unit 9 are internally mounted in a uniform diametric valve chamber 6 of the housing 6 to be high accurately assembled.