To provide a rotational/differential speed responding joint which can be easily assembled in a condition generating a positive pressure in an operating oil receiving chamber.

In an end face of a rotor 2, a filler hole 17 for injecting operating oil to an operating oil receiving chamber 10 is opened. In this filler hole 17, a closing screw 20 is screwed. Between a head part 20a of this closing screw 20 and an end face of the rotor 2, a seal member 19 which collides against the heat part 20a before its collision against the end face of the rotor 2 to seal between the filler hole 17 and the closing screw 20 is provided.