On the basis of the magnetic field intensity distribution of a magnetic field space (3), in order to homogenize the distribution, the positions and the volumes of magnetic material shims (such as shim bolts (27)) which have to be arranged on shim trays (17, 18) are first computed on a minute computational grid. Subsequently, from the distributions of the computed positions and volumes of the magnetic material shims, the local maximum values and local minimum values thereof are extracted, and the distribution areas of the volumes of the magnetic material shims with each value as the center are extracted. Then, the volumes of the magnetic materials distributed in the distribution areas are added. Finally, the results of the addition are displayed with the positions of corresponding local maximum values or the positions of corresponding local minimum values.
