PURPOSE: To enable the smooth discharge of foreign material and relatively hard garbage entered into a drainage pump by making the section of the hole of a discharge port provided on the casing body of the drainage pump into a nearly rectangular form extended over the full width of the outer circumferential inner wall of the casing body.

CONSTITUTION: A drainage pump 20 communicated with a sump part on its sump side is formed of a nearly cylindrical casing body 20a having, in its inside, a runner 22 mounted on the shaft of a drainage motor 21, a cylindrical intake port 20b having the same center as the shaft core of the shaft of the drainage motor on the anti-motor side of the casing body 20a, and a discharge port 20c tangentially provided on the outer circumference of the cylinder part of the casing body 20a, and the discharge port 20c has a nearly rectangular form extended almost fully in the lateral direction of the outer circumferential inner wall of the casing 20a. By this constitution, even if foreign materials and relatively hard garbage are entered into the drainage pump 20 at the time of drainage operation, they are carried along the outer circumferential inner wall of the casing body 20a by the rotation of the runner, and nearly certainly discharged from the discharge port 22c.