To control an output member to finite speed regardless of rotational fluctuation of an input member.

This device is provided with an input member with an eccentric rotor 2a, an output member connected in a relatively rotatable state to the input member and internally provided with a plurality of bores 4b arranged equally in a radial direction and oil chambers 3a connected with the bores 4b, a cylindrical piston 7 fillingly mounted in a linearly movable state in the bore 4b and provided with a flange 7a formed at the inner end, and a shoe 6 of nearly polygonal pillar shape fitted to the eccentric rotor 2a and formed in such a way that the outer plane 6a orthogonal to the center of each bore is extended in an axial direction. An annular land 6b brought into sliding contact with the flange face 7a of the piston 7 so as to periodically communicate each bore 4b, filled with operating oil, with the oil chamber 3a by its relative phase is protrusively provided on the outer plane of the shoe 6, and a control spring for energizing the piston 7 in a centripetal direction so as to impede the outflow of high pressure oil filled in the bore 4b as long as the output member 3 does not exceed the specified rotating speed is disposed in the bore 4b. The output member can thereby be controlled to the specified rotating speed regardless of the increase of rotating speed of the input member.