PURPOSE: To maintain a stabilized revolution by loading a normal conductive non-magnetic substance on a magnetic shield of superconductive material and providing a magnetic shielding member to the periphery of the non-magnetic substance.

CONSTITUTION: A normal conductive non-magnetic substance 12 is loaded on the central axial part of a magnetic shield 11 of a cylindrical superconductive material, and the magnetic shield 11 is coated with a magnetic shielding protector 7. The magnetic shielding member 13 of the cylindrical magnetic material is arranged on the periphery of the magnetic shielding protector 7 at a position corresponding to the non-magnetic substance 12. A part of magnetic flux 14 generated at a field winding 2 penetrates the non-magnetic substance 12 and reaches the magnetic shielding member 13. By the existence of this flux, the magnetic shield 11 of superconductive material does not slip along the axis because the force to pull it back is applied. Accordingly, the both ends of the magnetic shield 11 are not required to hold them so that the construction is made simple and the friction loss can be also reduced.