PURPOSE: To stably fix a pump having high discharge pressure and to prevent water leakage in the pump by providing a removable pump on a removable cylindrical part, and providing a seal step engaged with a seal surface and a turning-stopped part engaged with a turning-stop part on a pump casing for the pump.

CONSTITUTION: A guide slant face part 14 is formed on the inner periphery of a removable cylindrical part 13, and a pump housing 3 is guided along the slant face and stored. A seat surface C is seated on a seat surface 17, a turning- stop groove 8 is locked in a turning-stop projection 18, and rubber rings 7, 7 and seal surfaces 15, 16 seal between the pump housing 3 and a projection pipe 10. Even if an underwater pump D is operated in such a condition to generate high discharge pressure, moment which causes water leakage due to the discharge pressure will not work, and on the other hand, the underwater pump D can be stably supporting by a removable cylindrical part 13 fixed to the base P1.