To reduce shield current density by forming a superconducting coil section of a group of superconducting coils, a superconducting shield concentrically positioned on the perimeter of a group of superconducting coils in a cylindrical form laminated with superconducting thin films and superconducting shield coils positioned on both ends of a circular superconducting shield wound with a superconducting wire any number of times.

A superconducting shield 12 is formed in a cylindrical shape by laminating superconducting thin films and is concentrically positioned so as to cover a location slightly inside the whole length of the perimeter on which a group of superconducting coils are positioned. A superconducting shield coil 13 is wound with a superconducting wire any number of times at same diameter as the superconducting shield 12 and is circularly formed, and both ends of the superconducting wire are short-circuited to connect each other and are positioned at both ends of the superconducting shield 12. Accordingly, cyclic current occurs inside the superconducting shield coil 13 to cancel magnetic field applied to the superconducting shield coil 13 of magnetic field generated by a group of the superconducting coils 1 and shield current density at the end of the superconducting shield 12 is reduced.