PURPOSE: To supply water to a fish preserve, discharge water therefrom or supply water to a water jetting means without weakening the strength of a hull by simple operations.

CONSTITUTION: A water jet propelled boat is provided with a water introducing means provided to introduce water from the downstream of an impeller of a water jet propeller 3, a water introducing pipe 51 to supply water introduced from the water introducing means into a fish preserve 5 in a ship and a change- over means 7 to change over the condition of water introduced from the water introducing means to the fish preserve 5 to the condition of water not supplied to the fish preserve 5 and vice versa. The change-over means 7 is constituted to be changed over by an operating means 6 provided in a cab 2.