Abstract: A seal member includes: an inner circumferential surface surrounding a central axis; an upper surface connected to one end of the inner circumferential surface in an axial direction of the central axis; a lower surface connected to another end of the inner circumferential surface in the axial direction; and a protrusion that is provided continuously to the inner circumferential surface so as to surround the central axis and that includes a first portion inclined to the upper surface side toward one side in a circumferential direction of the central axis and a second portion inclined to the lower surface side toward the one side in the circumferential direction.

Abstract: In an eccentric radial piston pump, a rib 12 protruded in a radial direction is formed on an inner peripheral surface of an end portion on a discharge side of an eccentric cam ring 3 over a prescribed range. In an eccentric radial piston motor, a rib 12 protruded in a radial direction is formed on an inner peripheral surface of an end portion on a high pressure side of an eccentric cam ring 3 over a prescribed range. By the rib 12 formed in the radial direction, a rigidity of the eccentric cam ring 3 can be improved, and the eccentric cam ring can be prevented from being deformed by a thrust from the piston. Thus, the rigidity of the eccentric cam ring can be increased without increasing the thickness of the eccentric cam ring, and further the eccentric radial piston pump and the eccentric radial piston motor in which outside dimensions in the radial direction are reduced can be provided.