To discharge the air of the inside of a cylinder room without inviting the leak of an operation liquid.

Plural plungers 19 are arranged facing to a swash plate 16 integrated with a drive shaft 13. A pump is operated after push-pressing the plunger 19 in order by the swash plate 16. An air bleeding passage 51 opened/ closed by the plunger 19 is formed near the largest projected stroke position of the plunger end of a cylinder room 50. The air bleeding passage 51 is opened only when the plunger 19 stays near the largest projected stroke and the air in the cylinder room 50 is discharged. When the operation liquid is pressurized by the plunger 19, the air bleeding passage 51 is blocked by the plunger 19. Therefore, the operation liquid is not leaked from the air bleeding passage 51.