PURPOSE: To sufficiently lubricate a swash plate by allowing coolant gas to smoothly flow into a swash-plate chamber by introducing the inhaled coolant gas aslantly into the swash-plate chamber, in corresponding with the swing angle of the swash plate.

CONSTITUTION: The coolant-gas introducing means 26 and 27 for introducing inhaled gas from an intake passage 23 are installed at the front and rear edge parts of a swash-plate chamber 25. Said introducing means 26 is constituted of a coolant-gas guiding plate 38 and introduces the coolant gas along the swing angle of a swash plate 7. Said introducing means 27 is contituted of a flow- passage changing projection 31, and the coolant gas is introduced along the swing angle of the swash plate 7 from a through-hole 32. Therefore, lubricating oil is separated from the introduced coolant gas by the swash plate 7, and the lubricating oil sufficiently lubricates the lubrication position on the swash plate 7.