PURPOSE: To improve the safety by providing a limiting member limiting the rotating range of a throttle lever against a rotary plate and a means rotating the rotary plate in response to the action of a driver.

CONSTITUTION: When a motor 9 or an electronic control device 26 fails or a foreign object is bitten between a reduction gear 9 and a throttle lever 4 to cause an inoperative state, this abnormal state is detected by the output signal of an opening sensor 22, the excitation of a solenoid valve 191 is cut off, and an atmospheric hole 194 is opened. An accelerator pedal 17 is freely operated, and a driver operates the pedal 17 to open or close a throttle valve 2. The rotation of the lever 4 in the direction to open the valve 2 is limited when one end of the rotation range limiting window 4a of a rotary plate 7 is brought into contact with a stopper pin 13, thus the valve 2 is not opened by a motor 6 to the opening corresponding to the depression of the pedal 17 or above. The runaway of a vehicle is prevented.