When an accelerator pedal is released, or when a brake pedal is depressed and if braking force is lower than a reference braking force corresponding to a braking force immediately before causing a wheel lock, differential limiting force of a center differential is set to a predetermined value so as to retain an under-steer condition while engine brake is applied. When the brake pedal is depressed and if braking force is higher than the reference braking force, differential limiting force of the center differential is set to zero so as to assist an anti-lock brake system. Further, the reference braking force can be determined according to a road friction coefficient, a grade of road, a lateral acceleration and the like. Further, the predetermined value of the differential limiting force may be a constant value or may be a value corresponding to a front-to-rear weight distribution ratio.