PURPOSE: To obtain a propulsion force of a ship by utilizing the energy of rolling generated spontaneously by a ship to operate a pump so as to jet out the water.

CONSTITUTION: A water tank 1 is provided at the lower surface of the bottom of a vessel, ports 2 and 2 to suck and jet out the water from and to the water tank 1 penetrate through the walls, 11 and 11 of the bow and the stern, valve 3, 3, 3, and 3 are provided to the inner side and the outer side of the ports 2 and 2, and rotors 9 and 9, and handles 5 and 5 are connected through spiral shafts 8, 8, 8, and 8 and gears 4, 4, 4, and 4 to operate the valves 3, 3, 3, and 3.