PURPOSE: To improve of the operating efficiency by eliminating the excess and deficiency of an oil component in a mixed fluid discharged from a compressor part of cryostatic refrigeration equipment.

CONSTITUTION: A cryostatic refrigeration equipment 500 executes necessary cryostatic cooling by supplying a cryostatic cooling by supplying a cryostatic cooling machine 23 with a refrigerant body pressurized by a compressor 11. An oil separator 12C separates a mixed fluid 11a pressurized by the compressor 11 into oil 12b and the refrigerant body 12a. The separated fluids are cooled down by a refrigerant body heat exchanger 12D and an oil heat exchanger 12E respectively and then returned into the compressor part 11. Based on a detection signal 51a, a controller 53 controls a flow adjusting valve 52 so that the quantity of the oil 12b to be returned into the compressor 11 be made small when the oil 12b separated by the oil separator 12C is much and that the quantity of the oil to be returned is made large when the separated oil 12b is little. Since the excess and deficiency of the separated oil 12b are eliminated, invasion of the oil into the refrigerant body heat exchanger 12D and lowering of an operating efficiency due to the refrigerant body's bypassing the oil exchanger 12F are eliminated.