Abstract: A damper includes a housing, a hollow outer rotor provided inside the housing, an inner rotor disposed inside the outer rotor to constitute a plurality of liquid chambers and rotating in a state decentered relative to an axial core of the outer rotor, a communicating passage connecting between the liquid chambers, and a valve mechanism moving inside the communicating passage. Viscous fluid is filled between the outer rotor and the inner rotor. When the pressure inside the communicating passage reaches a predetermined value or above due to the rotation of the inner rotor, the communicating passage is closed or a flow passage area of they communicating passage is narrowed, and when the pressure inside the communicating passage falls to the predetermined value or less, the communicating passage is opened.

Abstract: An inner rotor 22 is rotated at a high speed, and if a pressure due to silicon oil S reaches a predetermined value or above, the pressure due to the silicon oil S traveling from a communicating passage 42 to a communicating passage 44, increases. Accordingly, a piston 52 is pressed toward a direction against an urging force of a coil spring 62, and abuts against a cap 64. Thereby, a circular groove 50 is divided, and the silicon oil S never flows to the circular groove 50 from a communicating opening 46, so that the communicating passage 42 and the communicating passage 44 become a non-communicated state. Then, a torque acting on the inner rotor 22 increases, and a damping force increases.