To generate uniformly the quench of superconduction over the whole of the strand of a meander-form material, by making larger the strand widths of both its end portions than the strand widths of its portions other than the same.

The strands of both the end portions of a meander-form material are the portions of connecting therewith copper electrodes, etc. When the sectional areas (strand widths) of both the end portions are made not larger than the sectional area (strand width) of the inside strand of the meander-form material, lowering the current-application characteristics of both the end portions owing to the heat generations caused by their contact resistances with the copper electrodes, the quenches of superconduction occur from both the end portions to make easy to burn and damage them, before the whole of the meander- form material transit to normal conduction. Therefore, it is necessary to make enough larger the sectional areas of both the end portions of the strand than the sectional areas of the portions other than the same. Concretely, it is desired to make the former not smaller than three times as large as the latter, even when the contact resistance of the strand with the copper electrode is reduced by using a silver strand. Also, when the sectional area of the connective portion between the inside strands is smaller than the one of the inside strand, since the quench of superconduction occurs from the folded portion of the strand to make easy to burn and damage the folded portion before the whole of the strand transits to normal conduction, it is necessary to make enough larger the sectional area of the folded portion than the one of the inside strand.