The fixed or variable displacement hydraulic motor-pump (1) includes a motor-pump central rotor (3) in which a hydraulic cylinder (14) is arranged, the rotor (3) being in sealed contact with an input-output spool valve (43) connecting the cylinder (14) with a motor-pump frame (2) while a hydraulic piston (13) moves in the cylinder (14) to push, using a hydraulic piston guided plunger (18), a tangential arm (22) articulated in the central rotor (3), and a tangential arm antifriction roller (28) on a motor-pump peripheral rotor (29) synchronized in rotation with the motor-pump central rotor (3).

A linear motion guide apparatus in which a guide rail can be readily provided with a meshing portion that meshes with a gear is provided. The linear motion guide apparatus includes: two guide rails that are movable relative to each other in a longitudinal direction thereof via at least one rolling element; and a cage configured to hold the rolling element and rotatably hold a gear engaging with a meshing portion provided to at least one of the two guide rails. The meshing portion includes a plurality of circular holes arranged in the longitudinal direction on the guide rail. Each of the circular holes has a wall surface formed in a cylindrical shape.