A superconducting coil is accommodated in a vacuum chamber. A radiation shield is arranged in the vacuum chamber with a prescribed space from the vacuum chamber to surround a periphery of the superconducting coil. A refrigerator cools the superconducting coil and the radiation shield by conduction. A provided member at least partly lies between the vacuum chamber and the radiation shield, through which heat is conducted from the vacuum chamber to the radiation shield. A cooling pipe has opposite end portions drawn out of the vacuum chamber and an intermediate portion in contact with the superconducting coil, the radiation shield, and the provided member. The provided member dissipates heat into a coolant flowing through the cooling pipe, to reduce the heat conducted to the radiation shield.