There are provided the steps of: measuring a magnetic field in a predetermined space and performing shimming by arranging a plurality of ferromagnetic shims in a superconducting magnet. The step of shimming includes arranging the plurality of shims at positions that make the magnetic field homogeneous, based on a result of measurement in the step of measuring the magnetic field and that provide a predetermined value of an electromagnetic force caused by the magnetic field to act on the plurality of shims.
