PURPOSE: To obtain a superconducting magnet apparatus wherein eddy current loss in an inner vessel is remarkably reduced and changing magnetic field acting on a superconducting coil is also reduced, by forming a discontinuous conductive metal coating layer on the inner vessel surface.

CONSTITUTION: When a copper-plated layer 10 is formed on the surface of an inner vessel 4, boundary lines 11 are formed in which stainless steel as the matrix of the inner vessel is peeled in the form that the copper-plated layer 10 is partially eliminated. Thereby the current path in the peripheral direction of the superconducting coil 3 is divided. A part where a large eddy current flows through a copper-plated layer 11 on the inner vessel 4 surface when changing magnetic field is applied to a superconducting coil 3 contained in an inner vessel 4 together with refrigerant is thickly formed, and a part where a small eddy current flows is thinly formed. Hence Joule heat loss due to the eddy current induced in the inner vessel container by the changing magnetic field is reduced, and the heat generation at the time of excitation can restrained to be low, so that the reliability of a superconducting magnet apparatus can be improved.