PURPOSE: To suppress quenching by hardening a resin filling the space section of superconducting winding by heating after removing not yet gelled resin filled in such spaces as grooves, holes, etc., formed among a supporting frame, spacers, and coil surfaces.

CONSTITUTION: After resin filling such spaces as grooves 6, holes 7, formed among a supporting frame 3, spacers 4 and 4a, and coil surfaces is removed before gellation, resin filing the space section of superconducting winding 1 is thermally cured. As a result, a coolant, such as liquid helium, etc., can be passed through the grooves 6 and holes 7 and a conductor can be cooled more efficiently. Therefore, even when local quenching takes place in a superconducting coil, the quenching does not spread over the entire body of the coil due to the cooling action of the coolant and the possibility of leaving of such a harmful material for insulation as rood's metal, etc., is eliminated.