To provide a highly reliable and inexpensive refrigerating unit and its operation method for preventing friction of a compressor and blocking-up of a pressure reducing device without a dryer even if moisture is mixed in.

This refrigerating unit constitutes a refrigerating cycle by successively connecting a refrigerating cycle apparatus including the compressor 1. Lubricating oil 8 of the compressor 1 uses hygroscopic oil. In a mechanism part of the compressor 1, a compound layer by nitriding is formed on at least its sliding surface. A temperature detecting means 13 is provided for directly or indirectly detecting the lubricating oil 8 or an environmental temperature on the inside and outside of the compressor 1 as a load characteristic value. A control device 15 is provided for controlling the compressor 1, a condenser 2 or the pressure reducing device 3 equipped as the refrigerating cycle apparatus on the basis of a detecting temperature of this temperature detecting means 13.