PURPOSE: To improve detection precision of failure of an electronic control type throttle by providing an upper limit value of a terminal voltage set and memorized in accordance with accelerator opening and accelerator opening changing ratio preliminarily, and a means to determine abnormality of a throttle actuator by using a detected terminal voltage value.

CONSTITUTION: A device is provided with a means 101 to detect accelerator operation quantity operated by a driver, a means 102 to detect changing ratio of the accelerator opening, and a means 104 to compute a desired throttle opening based on the accelerator opening and a vehicle running speed. It is also provided with a means 105 to control opening of a throttle valve based on the desired throttle opening, and a means 106 to monitor a voltage of a throttle valve drive motor. Abnormality of a throttle actuator is thus determined using the detected terminal voltage value, and an upper limit value of the terminal voltage preliminarily set and memorized, thereby failure detection precision is improved.