PURPOSE: To change the delivery amount of a refrigerant in accordance with the amount of super heat, by controlling an expansion member to be expanded and contracted in accordance with a change of temperature of the refrigerant, introduced into a low pressure chamber, so as to move a cam ring and changing the compression ratio.

CONSTITUTION: Sucked refrigerating gas 12 is allowed to flow into a low pressure chamber 9 in the front side, and a part of the gas is allowed to flow into a low pressure chamber 9 in the rear side from a bypass passage 16. The gas 12, being allowed to flow in the periphery of an expansion member 11, warms working fluid 13 sealed in the expansion member 11. Consequently, if the recirculative amount of refrigeration tends to be excessive with an over amount of super heat, the expansion member 11 expands to move a housing 1 of a cam ring against an adjusting spring 10 in the direction of eccentrically placing a rotor 3, and a compression rate is increased.