PURPOSE: To obtain a foreign materiel removing device which uses a water jet type propulsion machine which can be manufactured at a low cost and facilitates operation and is constituted so that a starter motor for the normal/ reverse revolution is connected with an engine, an impeller can be revolved reversely by the reverse revolution of the starter motor, and foreign materials can be removed by allowing the water in a water drum to flow reversely.

CONSTITUTION: As for a water jet type vessel propulsion machine which revolves an impeller 2 installed in a water drum 1 by an engine 3 and advances by jetting water rearward, a normal/reverse revolution starter motor 5 is connected with the engine 3, and the impeller 2 is reversely revolved by the reverse revolution of the starter motor 5, and the water in the water drum 1 is allowed to flow in the reverse direction, and used far removing the foreign material such as algae which intrude into the water drum 1.