To prevent the control ability from deteriorating due to a spring characteristic within a throttle valve opening degree range for normally controlling a throttle valve in order to ensure a throttle valve opening degree for siding a vehicle upon a failure of a device, and to simplify the stracture.
A throttle valve 2 is arranged to be rotated by an angle greater than 90deg. exceeding over a control angle range (about 90deg.) from a full closing degree to a full opening degree during normal engine operation, and the throttle valve 2 is rotated up to a position of a stopper 10 for limiting the rotation of the throttle valve at a predetermined angular position other than the control angle range by a spring 9 when a motor for driving the throttle valve, and is held at that position. Accordingly, the throttle valve can be set to an opening degree for siding, thereby it is possible to enhance the control ability of the throttle valve 2 by the motor 4, and to simplify the structure.
SUGIYAMA TAKESHI