PURPOSE: To freely control the movement of a hull by forming an annular body by setting the opposed sides among a plurality of square-shaped superconductive coils 1 and arranging said annular body in a hull and arranging at least a pair of electrodes, setting contiguous to the opposed side, in the water on the outer periphery of the hull.

CONSTITUTION: A triangular annular body is arranged in a hull, in the state where the opposed sides of square-shaped superconductive coils 1-3 are set contiguous. Electrodes 1A and 11A are arranged in water so as to be opposed to one opposed side 1a of the superconductive coil is through the wall of the hull. Other superconductive coils 2 and 3 are constituted similarly. When electric current flows in each superconductive coil 1-3, the coil magnetic field N is generated in the outward direction perpendicular to the coil surface, and the magnetic field between the contiguous coils is generated in the inward direction S. Therefore, the water stream in the direction perpendicular to the paper surface is generated in the sea water between the electrodes 1A and 1B and the electrodes 11A and 11B, according to the Feming's law. Therefore, the direction of the water stream can be changed in various directions according to the existence of application to each electrode and by the selection of the electrodes.