PROBLEM TO BE SOLVED: To provide a design method with excellent workability for a magnetic shield chamber of a strong magnetic field generator.SOLUTION: Magnetic plates 2, 3 are arranged on an indoor wall surface, and a wall surface shape R of a magnetic shield chamber 1 for suppressing a leak magnetic field to the chamber outside under a prescribed level and an arrangement position O of a strong magnetic field generator 5a are stored in a computer, A cycle of calculating arrangement amounts M of magnetic plates 2, 3 on the indoor wall surface to suppress the leak magnetic field switching an arrangement azimuth α of a device 5a around the perpendicular axis of the arrangement position O is repeated by the computer. Arrangement amounts M of the magnetic plates 2, 3 in each arrangement azimuth α of the device 5a to suppress the leak magnetic field by the magnetic plates 2, 3 with the least arrangement amount is acquired by comparing the arrangement amounts M of the magnetic plates 2, 3 in each azimuth α to each other. Preferably, switching the arrangement azimuth α using directional magnetic plates 2a, 3a, the arrangement azimuth of the magnetic plates 2a, 3a on the indoor wall surface for suppressing the leak magnetic field is calculated, and the arrangement azimuth θ of the device 5a for suppressing the leak magnetic field is determined from the arrangement azimuth of the magnetic plates 2a, 3a in respective arrangement azimuth by only the horizontally arranged magnetic plates 2a, 3a.
