A control unit for detecting an opening of an accelerator and an opening of the throttle valve to operate the throttle valve via a motor, sets a commanded value of an opening of the throttle valve at each of first predetermined cycles in accordance with an of the accelerator. A first opening/closing velocity is set in accordance with the set commanded value, a present opening of the throttle valve is read at each of second cycles shorter than the first predetermined cycles, the motor is rotated to open/close the throttle valve to follow a first predicted opening of the throttle valve until the opening of the throttle valve is smaller than the commanded value by a predetermined quantity, and the motor is caused to open/close the throttle valve to follow a second predicted opening of the throttle valve which is smaller than the first predicted opening of the throttle valve after the cycle when the opening of the throttle valve has been made smaller than the commanded value by a predetermined quantity. As a result, high-speed response of the throttle valve and prevention of overshoot can be realized.