Abstract: To make a motor to control throttle valve opening degree compact and reduce electricity consumption, a throttle valve lever (4) attached to a throttle valve shaft (3) has a roller (4b) and an operating arm portion (4a), a loosely fitted lever (8) is arranged to the throttle valve shaft (3), the operating arm portion (4a) is arranged in a gap (S) between first and second locking portions (8a1, 8a2) of the loosely fitted lever (8), a cam surface (7a) of a cam lever (7) connected to an output shaft (Ma) of a lead screw type step motor (M) faces to the roller (4b), a throttle valve operating drum (11) is coupled to the loosely fitted lever (8) via a link cover (13) and, when the motor (M) is driven, the cam lever (7) rotates the throttle valve lever (4) and the arm portion (4a) rotates within the gap (S) to hold an idling opening degree.