In a swash plate type hydraulic system such as a hydraulic pump, a hydraulic motor of the like, a group of cylinder bores in which plungers engaging a swash plate are slidably received are annularly arranged in a cylinder block, and higher and lower pressure oil passages are concentrically provided in the cylinder block. Further, a group of distributor valves are provided in the cylinder block in a radially arranged configuration for controlling the connection and disconnection between the higher and lower pressure oil passages and the group of cylinder bores by radial reciprocating motion of the valves, and an eccentric wheel is provided eccentrically with respect to the center of rotation of the cylinder block to abut against the outer ends of the distributor valves so as to impart a reciprocating motion to each of the distributor valves. A shifting device is provided for changing the eccentric relationship between the eccentric wheel and the cylinder block.