PURPOSE: To exhibit three characteristics consisting of high and low transmitted torque characteristics, and locking characteristic so as to reduce cost in a device where transmission torque is generated by utilizing the outflow districting effect of orifices, by changing the stroke position of a spool valve.

CONSTITUTION: A rotation difference induction type coupling generating transmitted torque in response to the rotating speed difference between front wheels and rear wheels has a rotor 12 provided with radially located drive positions diametrically reciprocating with the spherical contact faces being slidably in contact with cam faces, and as the drive pistons reciprocate, the volumes of piston cylinder chambers are changed. Then, in order to restrict the outflow of delivered oil flowing out from the cylinder chambers through delivered oil passages 14 to an accumulator cylinder chamber, first and second orifices 16a, 16b are provided, and thus three characterstics are obtained by changing the position of a spool valve 20 in which the second orifice 16b is formed.