PURPOSE: To enable to remove a trouble that the quenches of a pair of right and left superconductive coils are large without producing large electromagnetic force in lateral directions by electrically connecting the coils in series at every pair.

CONSTITUTION: When a pair of right and left superconductive coils 1, 1' are, as shown in Fig. (a), connected in series with each other and a circuit in which a permanent current switch 2 is commonly used for the coils 1, 1', is formed, the circuit is not entirely different, as shown in Fig. (b), at all from the conventional case in the ordinarily travelling state. On the other hand, since the currents which flow through the coils 1, 1' are simultaneously attenuated when a quench occurs at the one coil 1', as shown in Fig. (c), a null flux state is maintained, and a large electromagnetic repulsion force is not produced in lateral directions. Accordingly, a reason which causes a large trouble can be eliminated.