PURPOSE: To reduce the diameter of a rotor and to achieve a reliable excitation control by providing a heat radiation shield which has a high strength against electromagnetic force, has small dimensions in radius direction, and can reduce generation of eddy current.

CONSTITUTION: In the title rotor where a superconducting field coil winding 1 is wound around a coil winding mounting shaft 2 with a refrigerant storage part inside and then is cooled by liquid sodium store at the above refrigerant storage part, a plurality of grooves extended in axial direction are provided with a proper spacing at the outer periphery or the inner periphery of a high- resistance support cylinder 8 and a heat radiation shield 7 which is constituted by storing a bar 9 consisting of an improved conductive material at each groove is provided at the outer-periphery part of the superconducting field coil winding 1, thus reducing penetrating heat due to radiation to an extremely low- temperature part.