PURPOSE: To improve the maintenability of a centrifugal pump by enabling inspection and replacement of a packing easily without separation of a main shaft from an underwater bearing.

CONSTITUTION: Bellows 41 secured to a housing 22 of a centrifugal pump encloses the sleeve 11 of a main shaft 1 to be elastically axially extended or contracted, and has a packing retaining ring 42 secured at the end thereof. A packing 43 retained by the ring 42 is divided into plural sections, but is constructed to have no circumferential gap occurred and to be fixed to the ring 42 without rotation using knock pin, stopper screw or binder or the like. In inspecting or replacing the packing 43, the divided packings 43 are easily disassembled from the ring 42 and are then replaced with new parts by axially compressing the bellows 41 and providing space between the packings 43 and the packing retainer 32