PURPOSE: To improve traveling capacity as well as climbing capacity by braking a wheel when detecting the slippage of said wheel and suppressing the slippage.

CONSTITUTION: If a rear side left wheel 10c is caught in a muddy place and makes idle rotation, a slip signal from a number of rotation sensor 14 for left wheel 10c is inputted into a controller 16. The controller 16 outputs a braking signal, to feed oil pressure from an oil pressure controlling part 30 to rear sub- brakes 28c, 28d via a rear oil pressure feed passage 31b. Thereby, the idle rotation of the rear side left wheel 10c can be suppressed enabling torque to be transmitted to each of the wheels 10aW10d in the same condition that the slip had not occurred. Accordingly, if one wheel has slipped, the driving torque can be transmitted to the remaining three wheels enabling a car to be easily extricated from a muddy place.