PURPOSE: To inhibit the generation of an eddy current and to improve the workability by putting a bundle of many composite superconductive strands each having a layer of Ni or the like formed by plating in a pipe, reducing the diameter of the pipe and heat treating the pipe to form a shielding layer of Ni or the like around each of the strands.

CONSTITUTION: Many composite superconductive strands 12 each consisting of a shell of a stabilized base material 11 and a core of elements forming a superconductive substance 10 are plated with a nonmagnetic high resistance metal having higher electric resistance than copper, e.g., Ni to form a layer 13 around each of the strands 12. The plated composite superconductive strands 14 are bundled and put in a pipe 15 of a base material, the diameter of the pipe 15 is reduced and the pipe 15 is heat treated to diffuse the layers 13 to form a network shielding layer 17 of Ni or the like around each of the strands 14.