PURPOSE: To enable a throttle valve mechanism, operated in accordance with a condition of an engine, to surely accurately operate, by engaging the throttle valve opening mechanism, operated in accordance with a condition of the engine, with a lost motion lever.

CONSTITUTION: A lost motion lever 4 is secured to one end of a throttle valve shaft 2, to turnably support a transmitting lever 5, and a gear lever 51 is secured to the other end part. The lost motion lever 4 and the transmitting lever 5, having a connecting part 4a, are energized in a direction of engaging with each other by a lost motion spring 6 provided on the throttle valve shaft 2, to hook a return spring 7 of energizing a throttle valve 3 in a closing direction to the transmitting lever 5. The gear lever 51 has a location 51a engaged with a gear 52, to provide a mechanism that the transmitting lever 5 is not turned in the case of turning the gear lever 51 through the gear by an actuator 55. When the actuator 55 is inoperative, the throttle valve 3 can be turned by operating an accelerator, and when operated the actuator, the throttle valve 3 can be turned without changing a position of the transmitting lever 5.