To provide a liquid-operated motor with a reduction gear equipped with a rotary joint for smoothing the flow of fluid, and having compact structure.

A rotating frame 80, equipped with a liquid-operated motor 21 and a planetary gear reduction gear 22, and having an internal gear U, is rotatably arranged in the outer periphery of a motor housing 30. Peripheral surfaces 101 and 102 facing with a fine gap 100 are formed on the housing 30 and the frame 80, to form ringlike oil grooves 106, 107, and 108 on these peripheral surfaces. Fluid ports E1, E2, and E3; where each one end is communicated with the grooves 106, 107, and 108 respectively, and another ends are opened to the open end surface 33a of the housings 30; are drilledly provided, and also fluid ports F1, F2, and F3; where each one end is communicated with the grooves 106, 107, and 108 respectively, and another ends are opened to the outer peripheral surface of the frame 80; are drilledly provided on the frame 80 to constitute a rotation joint 85 by the housing 30 and the frame 80.