A heat exchanger (6) is housed in an indoor unit body (1) or a housing having a lower face opened. In the lower portion of the heat exchanger, there is disposed a drain pan (7) for receiving the drain water to be produced in the heat exchanger. In the indoor unit body, there is removably mounted a drain pump (10) for pumping up the drain water to accumulate in the drain pan, into the indoor unit body thereby to discharge the drain water to the outside. In the bottom wall portion of the drain pan, there is disposed a drain port (8) or an opening, into which the drain pump can be freely inserted. This drain port is closed in an openable manner by a drain cap (18).