PURPOSE: To improve volumetric efficiency by suppressing the temperature rise of gas, sucked into a low stage suction chamber and a high stage suction chamber, due to being heated by the heat entering from a high stage discharge chamber.

CONSTITUTION: A low stage heat insulating chamber 32 is formed between a low stage suction chamber 14 and a low stage discharge chamber 15, and a high stage heat insulating chamber 34 is formed between a high stage suction chamber 18 and a high stage discharge chamber 19. The low stage heat insulating chamber 32 and the high stage heat insulating chamber 34 are respectively connected to a radiator 38 installed outside a head cover so as to form a closed circuit, and secondary refrigerant is filled in this closed circuit.