To reduce frequency of grease supply maintenance for a drive shaft bearing part.

A drive shaft 22 for driving an impeller is rotatably supported on a hull via a bearing member 52. A grease reservoir 22f constituted of a ring-shaped recessed groove is provided on a facing surface 22e with the bearing member 52 in the drive shaft 22. A grease supply port 51d is provided on a bearing body 50 for storing the bearing member 52. Grease can be filled into a bearing chamber 51 and the grease reservoir 22f without extracting the drive shaft 22 from the bearing body 50.