PURPOSE: To enable heating of a compressor with no error derived from an external variable factor, by selectively controlling the flow of a fluid to a suction manifold from an outlet of a condenser according to the temperature of a compressed gas.

CONSTITUTION: When the temperature of a gas discharged from a compression chamber of a compressor 10 as detected by a temperature sensor 32 reaches a first projected temperature, an electronic controller 34 moves a solenoid valve 38 to an opening position so that a high pressure liquid refrigerant leaving a condenser 16 is injected into a suction manifold 52 of the compressor 10 from an injection port 62. The liquid refrigerant is evaporated and vaporized to cool both of a suction gas and the compressor itself, which lowers the temperature of the discharged gas as detected by the temperature sensor 32. When the discharge temperature detected by the temperature sensor 32 comes down below a value lower than a second projected temperature, the electronic controller 34 closes the solenoid valve 38. The first projected temperature is set lower than a temperature at which deterioration in a lubricating oil in the compressor 10 in particular occurs, and the second projected temperature is set at a value higher to prevent possible flooding of the compressor.