PURPOSE: To prevent the spin state at the time of a quick turn by inclining the center axis by a specific angle in the longitudinal direction against the vertical axis in a small speedboat provided with a jet nozzle at the bottom of a stern section and a steering nozzle rotatable around the center axis in the vertical direction.

CONSTITUTION: A jet pump 6 provided at the bottom of a stern section is connected to the rear end section of a drive shaft 5 extended to the stern direction from an engine stored in the hull of a small speedboat for leisure or the like. The jet pump 6 blows the water A sucked through the suction port 8 of a bottom section by the rotation of a propeller 7 backward through a jet nozzle 9 and a steering nozzle (rudder) 10, thus the driving force is generated. The steering nozzle 10 is rotatably supported on the jet nozzle 9 around the center axis 11A extended in the vertical direction, and it can be rotated to the right and the left. The center axis 11A is incrinatorily set at the angle 10-60° in the longitudinal direction against the vertical axis 16.