An indoor unit of an air conditioner includes a heat exchanger (6) accommodated inside a indoor unit body (1) which is a housing whose lower face is opened, a drain pan (7) which is disposed below the heat exchanger and receives drain water generated at the heat exchanger, a drain pump (10) which is detachably disposed within the indoor unit body, sucks drain water accumulated in the drain pan and discharges the drain water to the outside, a drain port (8) which is disposed at a bottom face wall section of the drain pan, the port being an opening portion through which the drain pump is insertable, and a drain cap (18) which openably closes the drain pump insertion port.