To provide a drainage pump for an air conditioner in which backflow water at the time of motor-stop is prevented from scattering on the side of the motor.

The drainage pump 1a comprises a pump main-body 10 having a pump chamber 16, an inlet 12, an outlet 14, and a cover member 130. A boss part 132 of the cover member has an opening 134 in which a shaft part 52 of an impeller 50 placed in the pump chamber 16 is protruded. An output shaft 64 of the motor 60 placed in a motor casing 140 is press-fit in the shaft part 52. When the motor 60 is stopped, water in a drain hose 18 flows backward into the pump chamber 16 to eject from the opening 134. In the motor casing 140, an outside peripheral wall 144 of the opening 142 for the outlet shaft 64 is tapered to prevent ejected water from invading the motor side.