To provide a defroster of an air conditioner for improving defrosting efficiency by securing a circulating quantity of a refrigerant of a temperature capable of heat exchange (defrosting) by returning the refrigerant to a compressor by discharging the refrigerant inside an outdoor heat exchanger when the refrigerant flowing in the outdoor heat exchanger becomes a heat exchange (defrosting) impossible temperature.

The high pressure high temperature refrigerant supplied via a defrosting bypass circuit 6 is defrosted and cooled by flowing in a part of the outdoor heat exchanger 3, and when becoming the heat exchange (defrosting) impossible temperature, the refrigerant is not allowed to flow in the outdoor heat exchanger, and is returned to a suction port 1a of the compressor 1 via a return bypass circuit 8, and is compressed again by the compressor, and is circulated in the outdoor heat exchanger via the defrosting bypass circuit so that the circulating quantity of the high pressure high temperature refrigerant is always properly kept, and dehumidifying efficiency is enhanced.