PURPOSE: To reduce the size of a device, by a method wherein high and low pressure oil chambers are annularly formed so as to surround the axis of a cylinder block and be arranged in the axial direction thereof, a number of distribution valves are annularly arranged concentrically to a plunger group to the cylinder block, and a valve swash is supported to the support system of a plunger swash.

CONSTITUTION: With a cylinder block 7 and a plunger swash (motor swash) 20 rotated relatively, each distribution valve 56 is reciprocated in the axial direction of the cylinder block 7 by means of a valve swash 62. A corresponding cylinder hole 18 is communicated alternately with high and low pressure oil chambers 46 and 47 to feed and receive working oil. Since a distribution valve 56 group is situated concentrically to a plunger 9 group, there is no need to increase the size of the axial direction of the cylinder block 7 in order to instal the distribution valve group and the plunger group. Besides, the valve swash 62 can be situated through utilization of a space around the plunger swash 20, and this constitution eliminates the need for increase of the size in the axial direction of a hydraulic device.