PURPOSE: To obtain a permanent current switch, which has a high critical current value, is small in off-heater power consumption, is high in exciting or demagnetizing speed and can be stably operated, by a method wherein the switch is formed by a method of winding a superconductive wire on a bobbin obtained by molding integrally a matrix resin and a reinforcing fiber having a negative expansion coefficient.

CONSTITUTION: A permanent current switch 7 is one formed by the method of winding a superconductive wire 9 on a bobbin obtained by molding integrally a matrix resin, such as an epoxy resin, and a reinforcing fiber having a negative expansion coefficient, that is, a negative expansion fiber. The negative expansion fiber is an organic fiber which is extended when a temperature is dropped from a room temperature, such as a polyethylene and a polyamide, and a carbon fiber and the like. Thereby, when the switch 7 is operated in a turn-ON state, the whole superconducting circuit can be stably operated and an increase of the resistance of the circuit can be made easily.