PURPOSE: To keep a motor part from the water flow of a water tank and set it to an air-cooled type so as to be used even with hot water by fixing a casing to a panel forming builtup water tank, and disposing the rotor part and the like of a pump inside the casing, and the motor part outside the casing.

CONSTITUTION: A casing 2 is fixed to a panel 1 forming a builtup water tank, and the rotor part 12, inlet port 14 and discharge port 15 of a pump are enclosed in the casing 2. A pump motor part 11 continued from the rotor part 12 is disposed outside the casing 1. The casing 1 and the inside of the water tank are communicated with each other by a communicating pipe 5, and a discharge pipe 17 is provided to distribute water from the discharge port 15. The communicating pipe 5 is provided in such a way as to make a detour outside the water tank, and a valve 6 is disposed at this detour part. The motor part 11 is thereby cut off from the water flow of the water tank and set to an air-cooled type so as to be used even if hot water is stored in the water tank.