PURPOSE: To ensure drivability in response to system fuel by comparing a plurality of throttle valve opening degrees with each other just before engine condition is transferred from an idling time to an off-idling time, and setting the throttle valve opening degree judged larger at the time of idling time.

CONSTITUTION: The whole of a device is provided with a first member 3 which is interlocked to an accelerator 1, a second member 7 following the first member 3 while being interlocked to a throttle valve 10, and a third member 15 driven by a motor 8. In this case, a throttle valve 10 is set to a first opening degree while maintaining a prescribed interval between the first member 3 and the second member 7 at the idling time. On the other hand, at the off-idling time, the throttle valve 10 is set to a second opening degree according to an accelerator opening degree by a sensor 5. Just before the engine condition is transferred from the idling time to the off-idling time, the first opening degree is compared with the second opening degree. As a result, when it is judged that the value of the first opening degree is larger than that of the second opening degree, the first opening degree is set.