PURPOSE: To make it possible to judge slips accurately by computing an acceleration ratio of the acceleration of a body with respect to the changing rate of rotation speed of a driving vehicle with time, and judging the slip based on the acceleration ratio.

CONSTITUTION: A throttle valve opening degree A, a rotary speed N of a crank shaft and a rotary angular speed ω of the output shaft of a transmission 13 are read out of the output signals of an accelerator sensor 18, a number-of-rotation sensor 17 and a vehicle speed sensor 19. Then, driving torque T is retrieved out of a three- dimensional table in a map pattern with the opening degree A and the speed N as addresses. With the speed N and the angular speed ω as addresses, a speed change ratio R is retrieved in a map pattern. The angular speed ω is differentiated, and a rotary angle acceleration ω' is obtained. Said acceleration ω' is multiplied by a rotating radius γ of a front wheel F, and an apparent acceleration αn is obtained. Then, the torque T is divided by the product of the rotating radius γ of the front wheel 16F and a vehicle weight (w), and a true acceleration αt is obtained. Then, the acceleration αn is divided by the acceleration αt, and an acceleration ration ratio (s) is obtained. The driving distribution ratio between the front and rear wheels 16F and 16R is controlled based on the acceleration ratio (s).