PURPOSE: To make it possible to arrange in parallel the magnetic field generated by a coil by a method wherein the coil, to be used for generation of magnetic field, and a cylindrical magnetic shield consisting of a superconducting material are joined together.

CONSTITUTION: Two superconducting coils 6 are arranged on both end parts in axial direction in the internal part of a doughnut-shaped cryogenic- temperature vessel 5. A cylindrical magnetic shield 7, consisting of a superconducting material, is provided between the above-mentioned two coils 6. A lead wire, with which the coils 6 are excited, is led out to outside the cryogenic vessel through the intermediary of a terminal, and the coils 6 and the shield 7 are dipped into the cryogenic-temperature medium 8 such as liquid helium and the like. Said coils 6 and the shield 7 are fixed using a frame 9, and the magnetic field generated by the current flowing on the coils 6 is formed into the line of magnetic induction in parallel with the axial direction of the cylindrical magnetic shield in the air-gap section surrounded by the shield 7 without bending the magnetic field toward the outside of the circumferential direction utilizing Meissner effect of the superconducting material.