PURPOSE: To move a plunger on the motor side along a tilted plate with high accuracy, to ease assembling work, and to simplify the reconstruction.

CONSTITUTION: Each of plunger rooms of a cylinder block 8 is provided with a spring 10. Each spring 10 pushes a plunger 11 from the cylinder block toward a tilted plate 12, so that a spherical end part 11a of the plunger 11 is energized to abut on a tilted surface 12a of the tilted plate 12 via a shoe 13, a thrust plate 14, and a thrust bearing 15. With this, the plunger 11 is projected smoothly from the cylinder block to move accurately along the tilted surface 12a, because of both extruding force by oil pressure and projecting/energizing force by the spring 10 when a motor (M) is driven by the oil pressure from a pump or because of the projecting/energizing force by the spring 10 when the motor (M) is rotated not by oil pressure.