A drainage pump includes a pump casing having an inlet and an outlet, and an impeller accommodated in the casing and rotated by a driving motor. The impeller has a plate-like vane. A liquid flows from the inlet toward a front end portion of the vane along the axis of the vane, and is discharged from the outlet in a direction substantially perpendicular to the axis of the vane. The front end portion of the vane has a convex shape, and therefore has an inclined portion which extends from a portion located on the axis of the vane to an outer peripheral edge thereof.

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