PURPOSE: To ensure an effective excitation for the large-current superconductive coil by giving an alternate conduction and heating to the heaters which are provided to plural number of superconductive wires featuring the high critical magnetic field and large critical current and then enclosing the magnetic fields sequentially to secure the pumping function.

CONSTITUTION: When conduction and heating is applied to heater 14 with the normal conduction given to superconductive wire 11, the magnetic field is led to superconductive circuit A formed with superconductive wires 11 and 12. With discontinuation of conduction for heater 14, wire 11 is turned superconductive again and the magnetic field is enclosed into circuit A. Thus, the current corresponding to the magnetic flux amount of the magnetic field enclosed flows to circuit A. Then when the conduction and heating is given to heater 15 with the normal conduction secured to wire 12, the current of circuit A flows to superconductive circuit B containing superconductive coil 13. With conduction stopped to heater 15, wire 12 is turned conductive again and the current flows to the superconductive circuit comprising wires 11 and 12 plus coil 13. Thus, coil 13 is excited. In this way, the pumping function is obtained by applying he conduction and heating to heaters 14 and 15 and enclosing the magnetic fields in sequnce, thus obtaining the fixed excitation at coil 13.