PURPOSE: To increase winding turns of a superconducting tape and improve performance and realize size reduction by a method wherein the end surfaces of the bobbin of a pancake coil are mutually coupled with neighbouring bobbins directly or with coupling rings between.

CONSTITUTION: A plurality of pancake coils 2 and 2' are arranged coaxially and protruded coupling parts 11 and recessed coupling parts 11' which are provided on the bobbins 1 of the pancake coils 2 and 2' are butted on each other and a large number of the winding frames 1 of neighbouring pancake coils 2 and 2' are couplied coaxially with each other with insulating spacers 5 between. Flanges 6 and 6' are attached to both the ends of the pancake coils 2 and 2' and are unified by fitting stay bolts 7 and the pancake coils 2 and 2' are tightened along the axial direction by pushing bolts 10 through springs 8 and pushing plates 9 and unified. with this constitution, a center pipe can be eliminated and the number of turns of a superconducting tape can be increased so that high magnetic field can be obtained and, moreover, the outer diameter can be reduced so that the necessary volume of the superconducting tape can be reduced and size reduction can be realized.