PURPOSE: To enable extremely fast control by providing a shell having an electrical insulating part on the outside circumference of a vacuum vessel and providing plural magnetic or magnetic flux sensors which detect the erroneous magnetic fields generated by the return current flowing along the electrical insulating part.

CONSTITUTION: Electric current is passed to plasma 18 and a poloidal magnetic field which is the perpendicular magnetic field in the Z-axis direction shown by an arrow 26 is applied simultaneously thereto from the outside in order to confine the plasma 18. While there is a method of using a poloidal magnetic field coil 20 and a shell 21 to generate such poloidal magnetic field, the functions are shared in such a manner that the shell 21 confines the plasma 18 for a short period of time and the coil 20 for a long period of time. The external poloidal magnetic field coil current is subjected to direct feedback control by measuring the erroneous magnetic field by the magnetic sensor or magnetic flux sensor 22. The eddy current of the shell 21 decreases with lapse of time and the external magnetic field which is the poloidal magnetic field is penetrated by said current, by which the magnetic field is maintained without being changed as a whole and, therefore, the plasma 18 is confined.