PURPOSE: To heat a low temperature rotary machine such as an expansion turbine and the like arranged in a liquifying refrigerator at a low cost in an efficient manner in a short time.

CONSTITUTION: A discharging part of a compressor 10 for circulating refrigerant is connected to an inlet of an expansion turbine 11 arranged in a refrigeration box 2 through a refrigerant supplying passage 16, and then an opening or closing valve 18 is arranged at the midway part of the refrigerant supplying passage. When the expansion turbine 4 is heated, the opening or closing valve 18 is opened and refrigerant of normal temperature discharged from the compressor 10 is directly supplied into the expansion turbine 11 through the refrigerant supplying passage 16.