A superconducting magnet apparatus obtains high magnetic field uniformity without increasing the volume of a magnetic material even against disturbances. The superconducting magnet apparatus has a circular superconducting coil (11) which generates a magnetic field a coil vessel (9) which contains the superconducting coil (11) together with refrigerant (14) a thermal shield (8) arranged so as to surround the coil vessel a vacuum vessel (3) with inside kept vacuum which surrounds the thermal-shield and magnetic materials (13) and for correcting the magnetic field, the magnetic materials being arranged in the vacuum vessel wherein the magnetic materials and are supported by a heat-insulation support medium (15) fixed to the coil vessel.
