PURPOSE: To quickly judge an acceleration slip regardless of the dispersion of the friction coefficient on a road surface by calculating the difference between the maximum and minimum wheel speed from wheel speeds, and judging as the acceleration slip when the speed difference or the temporal change rate of the speed difference becomes the respective preset value or above.

CONSTITUTION: A main throttle valve 4 and an auxiliary throttle valve 5 operated by an actuator 7 are provided on an engine 1. Throttle position sensors 8 and 9 are provided on opening sensors of throttle valves 4 and 5, detected signals are inputted to an electronic control device 12 together with four wheel speed sensors 13-16, and outputs are fed to an actuator 7 and a fuel injection valve 10. The maximum and minimum wheel speeds are selected from signals of sensors, the speed difference and the temporal change rate of the speed difference are calculated, when either one of them is the respective preset value or above, it is judged as an acceleration slip, the fuel injection valve 10 is once closed, and the auxiliary throttle valve 5 is quickly closed. Judgment is quickly performed regardless of the friction coefficient on the road surface.