PROBLEM TO BE SOLVED: To enable excitation and demagnetization of superconducting magnets in a plurality of cars at the same time by changing a disconnecting switch provided at the ground side to a circuit switch for series connection.
SOLUTION: In this exciting and demagnetizing circuit, if a superconducting magnet SCM is excited, a power lead detachable apparatus 3 is connected to the superconducting magnet SCM to be excited, a first switch 11 of a circuit switch 10 which is positioned on a connecting line of the superconducting magnet is closed to open a second switch 12 capable of short-circuiting both ends of the superconducting magnet, and current is supplied from an exciting power supply 4 to excite the superconducting magnet. When excitation is completed, a persistent current switch PCS is closed and current from the power supply is gradually reduced. When a persistent current mode is established, the second switch 12 of the circuit switch 10 is closed, the first switch 11 is opened and the power lead detachable apparatus 3 is disconnected. In the case of demagnetization, similar operations are performed.