This invention provides a superconducting magnet apparatus capable of preventing or restraining the heat invading into the apparatus and reducing the refrigeration load of an external refrigerator, at the time of changeover of a switch in transiting to a persistent current mode, and capable of quick changeover operation. In the superconducting magnet apparatus of the present invention (1), in transiting to a persistent current mode, a thermal superconducting switch (41) placed in a low-temperature domain and a mechanical switch (42) placed in a mid-temperature domain are turned on. Since the mechanical switch (42) is placed in the mid-temperature domain, even if a heat load is generated through the drive mechanism (60), it is not necessary to cool the mechanical switch to an extremely low temperature. In short, heat generated at the contact point of the mechanical switch (42) and heat invasion through the drive mechanism (60) are applied not to the low-temperature domain, but to the mid-temperature domain, so that an external refrigerator can easily absorb the heat load and the capacity of the refrigerator can be reduced.