To provide a power supplying system suitable for supplying electric power to the superconducting coil of a nuclear fusion reactor and which causes no disturbance with respect a commercial power system or does not require the commercial power system to have large power capacity.

A superconducting coil 10 is excited up to rated capacity with a thyristor converter 16 via a motor-generator 20 at the stage of the pre- excitation of the coil. At degaussing in the startup of core plasma, the energy of the superconducting coil returns to the motor-generator 20. Then, it is accelerated and dissipated. The large reactive power generated at the time of constant output is supplied from the motor-generator via a thyristor converter 18. Even if power for controlling the core is required unexpectedly, the required power is supplied by radiating the accumulated energy possessed by the motor- generator.