PURPOSE: To perform the drive of all wheels, that of rear wheels and the lockup of a differential through pumps and motors of small capacity, by providing freewheel valves and differential lockup valves between the pumps and the motors so that the valves can be optionally disconnected.

CONSTITUTION: Pumps P are driven by an engive E to supply pressurized oil to freewheel valves 14 and differential lockup valves 16 through changover valves 11. The freewheel valve 14 is connected to a front wheel drive motor Mf and shifted to disconnect the motor Mf from the pump P to make wheels free. The differential lockup valve 16 is shifted to supply pressurized oil through orifices 16b so that the oil flows through motors Mf, Mr. According to this constitution, touque can be transmitted to one wheel even if another races.