PURPOSE: To eliminate a long drain pipe and decrease an expenditure of work by a method wherein drain dewed in an indoor heat exchanger is received by an inclined drain pan in the indoor unit and sent to an upper sprinkler of an outside heat exchanger, the drain is sprinkled to be vapored and the non- vaporized drain water is evaporated by an electrical heater.

CONSTITUTION: Dew is formed at an indoor heat exchanger 32 and drain water is dropped into a drain pan of an indoor unit. The dropped drain water is flowed in a pipe 34 arranged to turn in front of an entire heat exchanger 30, flowed in the pipe 29a of the sprinkler 29 and then sprinkled to the indoor heat exchanger 26. The water is heat-exchanged with a condensation heat with this sprinkling action, the drain is evaporated, and the vapor is discharged out of the house through a discharging port by an outdoor blower unit 25. The non-evaporated drain is dripped into a drain pan of an outdoor unit. The dripped drain is heated by an electrical heater 28 and evaporated and flowed in the heat exchanger of the outdoor unit together with the surrounding air in the discharging flow passage flowing from the surrounding air suction port 37, passed through the outdoor blower 25, and discharged out of the house through the discharging port.