PURPOSE: To suppress heat generation at various parts of a power train while a stationary number of rotations of front and rear wheels is produced when tires of different diameters are installed, etc., by monitoring the temperature of oil of a differential gear for an applicable vehicle and changing over to a low transmitting torque characteristic side when a detected differential gear oil temperature value is high beyond a specified limit.

CONSTITUTION: A rotation-differential sensitive type joint (a) suppresses flowing out of delivery oil flowing out by pumping action through an orifice to increase a pressure in an output oil chamber and generate a transmitting torque to distribute it to either one of the drive systems according to a difference in the number of rotations of front and rear wheels, when the 1st and 2nd rotation members are rotated relatively to each other according to a difference in the number of rotations of the front and rear wheels. A transmitting torque characteristic changeover control means (e) changes over a transmitting torque characteristic alteration means (b) from a high transmitting torque characteristic to a low transmitting torque characteristic, when the detected differential oil temperature value of a differential oil temperature detecting means (d) for detecting the oil temperature of a differential (c) on the direct-coupled drive wheel side of a vehicle is high beyond a specified limit.