To prevent a thin thread-like entered matter from being wound around an underwater rotating shaft.

An impeller 10 and a diffuser 11 are provided within the pump casing of a water jet propeller. The impeller 10 is fixed to a drive shaft 12 through a flange 21. The end surface of the impeller 10 is opposed to the end surface of the diffuser 11 with a minute clearance. A rope guard 23 provided on the circumferential edge of the end surface of the diffuser 11 is opposed to the end surface of the impeller 10 with a minute clearance. In the inside of the rope guard 23, a rope cutter 24 is fixed to the flange 21. The cutting edge of the rope cutter 24 is situated in the clearance between the impeller 10 and the diffuser 11 on the inside of the rope guard 23, and turned to the rotating direction of the impeller 10. In operation, the rotating rope cutter 24 shortly cuts slender foreign matter entered between the impeller 10 and the diffuser 11 through the clearance of the rope guard 23. Thus, the entered matter is never wound around the drive shaft 12, and an oil seal 26 can be prevented from being damaged.