PURPOSE: To provide a magnetic field generator equipped with a quench protection device which can both control a magnetic field to the best of its ability and safely stop only a superconducting coil where a quench occurs and a coil used to protect a quench when a quench occurs in a superconducting coil in a magnetic field generator including superconducting coils with magnetic coupling.

CONSTITUTION: When a quench occurs in a superconducting coil 11, supplied current 14 is attenuated through a resistance 15 by opening a circuit breaker 14. On the other hand, the current flowing through the superconducting coil 11 during the occurrence of a quench is changed in route with a normally conducting protection coil 12 magnetically coupled with a superconducting coil 11 almost completely by closing a supplier 16, and is attenuated with a protection resistance 17.