PURPOSE: To give an optimum throttle valve opening characteristic for stable operation, by changing lever ratios, that is, ratios of the distances between engaging places of two throttle valve levers with a transmission lever and the center of turning of the transmission lever, and optionally changing the relation between the amount of operation of an accelerator pedal and the opening of a throttle valve.

CONSTITUTION: When a lever shaft 9 is rotated in response to the amount of operation of an accelerator pedal, a throttle valve shaft 4 is rotated through two throttle valve levers 5, 12 and a transmission lever 14 to open a throttle valve 3. Then, when an actuator 20 moves the transmission lever 14 in response to the operating conditions of an engine or a car, the eccentric distances between the throttle valve shaft 4 / the lever shaft 9 and the center of turning of the transmission lever is changed, and lever ratios of the transmission lever 14 to the two throttle valve levers 5, 12 are changed in response to the eccentric distances. As a result, the opening of the throttle valve 3 with respect to the amount of operation of the accelerator pedal can be optionally changed in response to the operating condition.