To move accumulated dust to a portion with weak inlet current and wash it away with a current at the bottom of the ship, enabling an automatic cleaning, by providing a screen device movable in the direction perpendicular to the direction in which the ship forwards at a jet inlet of a water jet propelled ship.

A screen 6a having a width of approximately twice that of an inlet port is installed slidably in the lateral direction perpendicular to the direction in which the ship forwards at the inlet port of the bottom of the water jet propelled ship. The front and rear portions of the inlet port 7 are sandwiched by a guide 8 provided at the bottom of the ship, and the lower surface of the screen 6a is brought into slide contact with a blade edge of a scraper 9 that is attached to the guide 8. When floating matter reaching the screen 6a is striplike long mutter or thin film vinyl, they are cut by the scraper 9 having a blade edge in contact with the screen 6a at the left and right sides of the frame of the inlet port 7, and can be removed without being attached to the screen 6a. Therefore, by operating the screen device continuously or intermittently while the ship is sailing, automatic cleaning with high workability is achieved.