PURPOSE: To improve the efficiency of an electromagnetic induction prime mover by composing to act a magnetic field and a current to an annularly sealed fluid.

CONSTITUTION: A passage 1 is annularly formed, and mercury 2 is circulated as a sealed fluid. The passage 1 is composed of an acceleration section 3 having a small sectional area and a circulating section 4 having a large sectional area, a superconducting magnet 5 and electrodes 6 are provided in one of the sections 3, 4, and a water wheel 7 is provided in the other. The wheel 7 is rotatably provided through an attachment plate 17, its output shaft 15 is penetrated watertightly through a passage wall 12, and connected to a screw propeller. Thus, an electromagnetic induction prime mover acts a magnetic field to the fluid 2 in the passage of the magnet 5, the electrodes 6 supply a current to the magnetic field acting region to act a force to the fluid 2 of this region. As a result, the fluid 2 is circulated in the passage 1 to rotate the wheel 7 provided in the passage 1.