To provide a self-priming pump not needing connection of an internal suction pipe inside an enclosure of a water heater or the like, capable of having an external suction tube directly connected at the lower edge of the enclosure.

A pump cover 3 which is a resin composition of the self-priming pump has a suction tube connecting part 28' protruding toward the lower center, and a connecting tube passage 40, for communicating to each other the suction tube connecting part 28' with a central introducing space H' of a closed annular groove facing the center of a centrifugal type impeller 15, passes through a water collecting chamber 12 at a shortest distance. An opening 40a of the connecting tube passage 40 is positioned at the substantially highest part of the outer peripheral contour of a thrust bearing part 11.