To freely relatively rotate a housing and a rotor both when rotational speed becomes higher than a specified one.

A valve storage hole 62 forming a part of an inlet path 6 interconnecting a plunger chamber 46 and an operating oil storage chamber is formed in a rotor 3. An axis of this valve storage hole 62 is almost orthogonalized with a rotational axis L between a housing 2 and the rotor 3. This valve storage hole 62 is provided with a check valve 9 which checks a flow of operating oil from the plunger chamber 46 to the side of operating oil storage chamber, but allows a flow of the operating oil into the reverse direction. Energizing force of a valve spring of this check valve 9 is set up to be small than centrifugal force acting on a ball valve when a joint 1 turns at a high speed of more than the specified revolution.