PURPOSE: To prevent the occurrence of cavitation and to improve water suction performance by moving a part, located in the vicinity of a suction port, of an intake duct, the suction port of which is formed in a ship's bottom, in a direction crossing the axis of the intake duct at right angles, and varying the opening area of the suction port.

CONSTITUTION: An intake duct 10 of a water jet pusher is formed in a manner to obliquely upwardly extend from a suction port 12, formed flush with a ship's bottom 11, toward the rear of the ship bottom, and a pump impeller is coupled to an outlet part 13 of the duct 11. In this case, a duct seat 14 is suspended toward the ship's bottom 11 toward the side, positioned facing the ship's bottom 11, of a portion ranging from the suction port 12 of the duct 10 to the outlet part 13. A portion extending from the duct seat 14 to the outlet part 13 forms a moving duct surface 15. By actuating an actuator 21 to move an actuating rod 20 in the direction of the flow of a boat, the inclination angle of the moving duct surface 15 is changed, and by moving the lower end part of the moving duct surface in the longitudinal direction of the boat, the opening area of the suction port 12 is varied.