PURPOSE: To simplify a mechanism, to facilitate miniaturization, and to perform smooth and precise control of a flow rate.

CONSTITUTION: A plurality of cylinders 12 are formed in a cylinder block 10 mounted on a rotary shaft 8 and a piston 16 is contained in each cylinder. The rotary shaft 8 is relatively rotated based on a valve plate member 26 and a swash plate 42 and during the relative rotation, a distance between the part, corresponding to each cylinder 12, of the swash plate 42 and a cylinder 12 is changed in the axial direction of the cylinder. The piston 16 is energized toward the swash plate 42 through the force of a compression coil spring 18. A fluid suction opening 28 and a fluid delivery opening 30 are formed in the valve plate member 26, and the cylinder 12 is communicated alternately with the fluid suction opening 28 and the fluid delivery opening 30. The swash plate 42 is relatively rotatable based on the rotary shaft 8 and rotated by a swash plate rotation operating member 48.