PURPOSE: To ensure reliability of a compressor with a low temperature side refrigerating cycle in a dual refrigerating apparatus using a refrigerant other than carbon fluoride chloride.

CONSTITUTION: In a low temperature side refrigerating cycle S2 of a dual refrigerating apparatus, a refrigerant is used as mixture of R23 as main refrigerant and R22 as sub refrigerant with a boiling point thereof higher than the main refrigerant. A gas discharged from a compressor 7 is cooled with a cooling unit 9 down to a temperature at which the R22 is condensed but the R23 is not and a refrigerating machine oil and the R22 are separated with a gas/liquid separator 10 from the R23. The refrigerating machine oil and R22 separated with the gas/liquid separator 10 are returned to the compressor 7 through a liquid return pipe 14. The compatibility between the refrigerating machine oil and the R22 achieves higher recovery rate of the refrigerating machine oil with the gas/liquid separator (10) and the returning of the refrigerating machine oil to the compressor (7) from the liquid return pipe (14) achieves higher reliability of the compressor (7).