PURPOSE: To enhance reliability, by setting a 'U'-formed connecting case made of conductive material, for the coil connecting device of superconductive field coils.

CONSTITUTION: The connecting device of superconductive field coils 1 is provided with connected sections 3, by soldering, and a groove 12 containing the superconductive field coils 1 is formed and is provided with a 'U'-formed connecting case 11 made of conductive material for being connected by soldering. Accordingly, the connected sections 3 are composed of the three surfaces of the groove 12 of the connecting case 11, and are connected to. As a result, the connecting case 11 is used for the passage of current, and so connecting resistance can be reduced.