To achieve an integration of components and the rationalization of the default opening mechanism of the throttle valve, a reduction of the load of the motor drive and a stabilization of the throttle control operation. In a default opening setting mechanism with which the default opening of the throttle valve 24 is maintained to be larger than the fully closed position when the electric current does not pass through the motor 12 driving the throttle shaft 18, the throttle lever 3 and the sleeve 45 are inserted and fixed, and the sleeve 42 united together with the return lever 2 is engaged with the sleeve 45 so as to be enabled to rotate in relative to the sleeve 45. The sleeve 42 is energized by the return coil in the close direction of the throttle valve 24 up to the initial opening position. This energized operation enables the return lever 2 to be coupled with the sleeve 3. A force for opening the valve for keeping the default opening the throttle valve 24 is energized by the spring 5 onto the throttle shaft 18 near the fully closed position.