PURPOSE: To lengthen the life-time of a heat exchanger by using operational oil for the compressor cooling agent of a freezer.

CONSTITUTION: Oil pump 2 is driven by input shaft 8, and operational oil flows from outlet passage 5 formed inside oil tank 1, passes passage 22, and is branched into three streams. One of them passes passage 60 and is sent to oil-pressure chamber 33. Another is sent to passage 200-orifice 201-drive side chamber 210 and returns to oil tank 1. A thrid passes passages 61 and 63, flows to gap 441 at the lower side of heat exchanger 44, passes passages 63' and 64 formed around compressor chamber 45, flows to gap 441 at the upper side of heat exchanger 44, and here it gets heat from the high-pressure gas; then it returns to oil tank 1 via passages 64 and 62, where it is cooled by the water supplied by heat exchanger pipe 100, and then, it is circulated again.