PROBLEM TO BE SOLVED: To efficiently discharge residual water in a drainage pump provided in an indoor unit of an air conditioner.SOLUTION: A drainage pump 1a has a rotary blade 20 in a pump housing 10, and is driven by a motor 30. A motor lower case 100 attached to an upper part of the pump housing 10 and supporting the motor 30 includes an inner cylinder part 120 and an outer cylinder part 105. Water returned from a water pumping pipe in stopping of the pump is ejected from an opening part 116 of a lid part 110. Residual water Won an upper surface of the lid part 110 is drained from an inner cylinder slit 122 and a drainage slit 130. At that time, the residual water Wis smoothly discharged to the outside by the effect of surface tension induced by a guide member (projection) 140.