To allow malfunction detection reliabile and excellent in quick response and prevent the failure of malfunction detection following a change in target value.

Throttle sensors 15, 16 detect a throttle opening in double. An ECU 20 calculates the target opening of a throttle valve 13 in accordance with various input signals and feedback controls the drive of a motor 14 in response to a deviation between the target opening and an actual throttle opening (a sensor detected value). The ECU 20 performs malfunction detection for the throttle sensors 15, 16 in accordance with the rate of a change in sensor detected value and then sets a malfunction criterion value to be variable with a change in target opening. Specifically, the transient malfunction criterion value following a change in target value is changed with respect to the steady- state malfunction criterion value when the throttle opening is converged to the target value.