PURPOSE: To make a reversible pumpturbine and a generator-motor unnecessary and to improve the generator efficiency by providing a headrace with a pair of positive and negative electrodes and a superconductive coil as pumping apparatus for the purpose of performing a pumping operation and by causing DC to flow through these parts.

CONSTITUTION: At the time of a pumping operation, inlet valves 9 and 5 are turned OFF and DC from a DC supply source is caused to flow from a positive electrode 12 to a negative electrode 13. Also, when a current is caused to flow through a superconductive coil 14, DC flows between the positive and negative electrodes 12, 13 of the headrace 3 via sea water. Further, a downward magnetic field is generated in the superconductive coil 14, a force directed in the direction of the arrow C is generated in sea water by the DC and magnetic field so that energy of movement is generated, and sea water flows through a conducting iron pipe 4 from the headrace 3 to be stored in an upper reservoir 1. When the inlet valves 5 and 9 are turned OFF at the time of operation of a water turbine, sea water flows into the water turbine 21 to give it motive power and a generator 22 converts the motive power into an electric power to generate electricity.