PURPOSE: To improve COP and compact the size of equipment by spraying different circulation oil in a respective actuation gas flow of a compressor and an expander and separating gas from said circulation oil directly after it is sprayed, and using the gas and the oil separately for radiation and refrigeration, and allowing both the gas and oil to be recirculated by a jet pump.

CONSTITUTION: Cyclones 12, 13 for air and oil separation are installed to gas outlet passages 10 and 11 from a compressor 1 and an expander 2 respectively. A greater portion of liquid droplet is arranged to flow from flow down pipes 1 and 15. Then, the gas which has dropped most droplet at the cyclones 12 and 13 is introduced into an expander inlet passage 8 and a compressor inlet passage 6 by way of flow passages 18, 19, 20, and 21, 22, and 13. The circulation oil which flows down in the flow down pipe 14 from the cyclone 12 is fed again into a jet nozzle 7 from a compressor side oil jet pump 27 by way of a radiator 26 and a recirculated. The circulation oil which flows down in the flow down pipe 15 from the cyclone 13 is fed back to a jet nozzle 9 by way of an oil jet nozzle 29.