the maximum empirical magnetic field for one superconducting coil is too large to form a superconducting coil the coil can be divided into more than one coil as in this embodiment to reduce the electromagnetic force or the maximum empirical magnetic field the present invention also meets the following condition to reduce the leakage magnetic field from the divided coils as described above the superconducting main coils are defined to have a positive current direction the shield coils 280 281 of positive current directions make up a first group of shield coils the shield coils 282 283 of negative current directions make up a second group of shield coils u03b81 is defined as an angle 287 between the z axis 284 and a half line 286 extending from the origin 285 to the cross section geometric center 290 of the shield coils 280 281 of the first group u03b82 is defined as an angle 289 between the z axis 284 and a half line 288 extending from the origin 285 to the cross section geometric center 291 of the shield coils 282 283 of the second group the u03b81 u03b82 are in a relation of u03b81 lt u03b82 and the corresponding groups of shield coils have.