PURPOSE: To change displacement continuously with simple structure by switching a communicating passage between a swash plate chamber and an intake chamber according to heat load, and communicating a chamber, located between the tip part and body part of a piston reciprocated by the rotation of a swash plate, with the swash plate chamber.

CONSTITUTION: When intake pressure becomes lower than the specified value with the change of heat load, switching valve mechanism 24 is placed in the valve closed state, and passing through a gap between the outer peripheral surface of a piston tip part 12a and the inner peripheral surface of a cylinder bore 11, a blow-by gas flows into a chamber 18 from a compression chamber 27 and shut up in the chamber 18 and a swash plate chamber 13, resulting in pressure rising. At the time of an intake stroke, a piston 12 is moved together with a swash plate 8 to start intake, but because of the pressure in the chamber 18 being larger than that in the compression chamber 27, the piston tip part 12a stops after a slight stroke, and thereby the intake quantity is reduced in large degree. At the time of a compression stroke, the piston tip part 1a is not moved until being hit by a piston body 12b, and thereby the stroke quantity of the piston 12 is reduced to result in displacement decrease. Whereas, at the time of the intake pressure being over the specified value, the displacement is increased.