PURPOSE: To save energy by controlling parallel solenoid valves of a refrigeration circuit by means of a thermostat for detecting lubricating oil temperature 50 as to keep the compressor temperature at a proper level.

CONSTITUTION: When the temperature of lubricating oil 2 is relatively high in the summer season, a solenoid valve 4 is kept in an open state by means of a thermostat 9. Accordingly, the most part of refrigerant flows via the first refrigeration circuit to a condenser 5 due to a difference in the resistances of the flow passages of the refrigeration circuit, and refrigerant gas flows through a lubricating oil heating pipe 3 of the second refrigeration circuit, very slightly heating the lubricating oil 2. On the contrary, when the temperature of the lubricating oil 2 is low in the winter season, the solenoid valve 4 of the first refrigeration circuit keeps a closed state, and all high temperature refrigerant gas discharged from the compressor 1 flows through the lubricating oil heating pipe 3 of the second refrigeration circuit to heat the lubricating oil 2, allowing proper temperature to be kept.