In a step of inserting each of a plurality of disk-shaped windings into a recessed groove portion of a corresponding one of a plurality of ring-shaped fixing portions, each of the plurality of disk-shaped windings is inserted in a state where an outer circumferential surface of each of the plurality of disk-shaped windings is spaced apart from a bottom surface of the recessed groove portion of a corresponding one of the plurality of ring-shaped fixing portions. In a step of bringing the outer circumferential surface of each of the plurality of disk-shaped windings into direct or indirect contact with the bottom surface of the recessed groove portion of the corresponding one of the plurality of ring-shaped fixing portions, each of the plurality of disk-shaped windings and an outer frame portion are cooled and contracted for contact.