PURPOSE: To dispose drain by a method wherein drain is stored and sprinkled over an outdoor heat exchanger to evaporate it during cooling operation, and drain atomized by a rotating disk is led into an indoor unit to help humidifying during heating operation.

CONSTITUTION: During heating operation, drain drips down along an outdoor heat exchanger and gathers into a reservoir 9. The drain W is atomized by a rotating disk 7a, a damper 15 provided on a partition wall 12 is opened to introduce the atomized drain into an indoor unit 1a, and it is blown out by an indoor fan 12. During cooling operation, drain is led from the bottom plate of the indoor unit 1a to the reservoir 9 through a drain pipe 8, and splashed by the rotation disk 7a rotating at a half rotational speed to sprinkle it over the outdoor heat exchanger 3, so that drain is evaporated and disposed by heat into the atmosphere.