PURPOSE: To hold transfer torque at an adequate value all times by controlling a variable throttle valve in an oil passage, communicating with the discharge port and the suction port of a hydraulic pump which controls transfer between front and rear wheel drive shafts, in relation to the output of an oil temperature sensor.

CONSTITUTION: Drive torque from the first rotational movement shaft 11 is transfered to the second rotational movement shaft 14 via a vane pump for a drive connection device 13 which is made up with a rotor 21, a vane 21a, a cam ring 22, side plates 24, 25. This transfer force is controlled by the opening of a variable orifice which contains a valve room 40a, a vale element 40b and a solenoid 40d installed in an oil passage, communicating with the suction port 27a and the discharge port 27b of the vane pump, i.e., by the variation of reflux. The throttle quantity of the variable orifice is controlled in relation to oil temperature detected by a temperature sensor 50, i.e., reflux oil quantity is corrected by the oil temperature to hole set transfer force. It is thus possible to hold transfer torque at an adequate value all times.