PURPOSE: To decrease a discharge temperature during a high loading operation and prevent a deterioration of coolant oil and coolant by a method wherein a liquid accumulation piping is arranged between an outdoor heat exchanger and an expansion device and the liquid accumulating piping is heat exchanged with drain water fed from the indoor heat exchanger.

CONSTITUTION: A compressor 1, an outdoor heat exchanger 2, an indoor heat exchanger 3 and capillary tubes 4 and 5 acting as an expansion device are arranged and a liquid accumulation pipe 13 with its extremity end being closed is arranged at the connection part 12 to which the capillary tubes 4 and 5 are connected. A water reservoir 15 is arranged at the bottom part 16, an extremity end of the drain hose 14 is fixed to cause the flowed water to be accumulated in the water receptacle 15 and the extremity end of the liquid accumulation piping 13 is placed in such a way as it may be immersed in the drain water in the water receptable 15. With this arrangement, in case of performing an operation under a high load, the coolant liquid accumulated in the liquid accumulating pipe 13 is evaporated to become an over-heated vapor, an amount of circulated coolant in a refrigeration cycle is increased and in turn a discharging temperature is decreased.