PURPOSE: To hold the opening of a throttle valve at a proper value during ordinary operation and during the occurrence of abnormality, such as failure in operation of a motor, and to use a comparatively small electromagnetic coil.

CONSTITUTION: A throttle valve 3 is fixed on a shaft 4 in a manner to be capable of opening and closing an air passage 2a of an internal combustion engine. A driven gear 14 rotated with the aid of a motor 13 according to an accel opening signal and an acceleration link 25 rotated in linkage with operation of an accelerator are arranged on both sides of a clutch disc 5 fixed to the end part 4a of a shaft 4. A pin 9 energized to the acceleration link 25 side through the force of a spring 8 is contained inside the clutch disc 5 selectively coupled to the driven gear 14 or the acceleration link 25 by means of an electromagnetic coil 7. A hole 26 engaged with the pin 9 is formed in the driven part 28 of the acceleration link 25. During the occurrence of abnormality to a motor, etc., the pin 9 and the fitting hole 26 intercouple the clutch disc 5 and the acceleration link 25 when the phase of the clutch disc 5 coincides with the phase of the acceleration link 25.