PURPOSE: To prevent oil leakage of check valves by locating check valves for controlling the flow of the oil of an hydraulic pump in the axial center position of the rotation of an input side rotating member and an output side rotating member.

CONSTITUTION: A first and a second check valves 87, 88 for respectively allowing the only flow of the oil from the low pressure oil chamber 89 side to gear pumps P1-P4 side are interposed near the low pressure oil chambers 89 in a first and a second oil circulation passages 83, 84. The first check valve 87 is a ball type one-way valve which consists of a valve seat 91 formed in the axial center of the rotation of a first inside gear member 52 and a spherical valve member 92 housed in the valve member 91. With this structure, even if the first inside gear member 53 is rotated, the centrifugal force is not generat ed in the valve member 92 of the first check valve 87 to eliminate generation of oil leakage. Since the valve seat 91 and the first oil circulation passage 83 are formed by drilling the wall surface of the first inside gear member 53 in the thickness direction, the processing is facilitated, and the second check valve 88 is similar to the first check valve.