Ferritic stainless steel(HT-9) is a prospective candidate for a first wall material of a fusion reactor. It experiences magnetic stress due to magnetization in magnetic field. A ferromagnetic cantilever of mild steel was provided to carry out a test on magnetomechanical behavior and to compare with theoretical prediction. The theoretical prediction was made for an infinitely wide beam plate and magnetic stiffness was taken into account. Field distribution of the finite specimen is very different from one of an infinite specimen. It is made clear that deformation is proportional to the squared field for smaller applied field while linear with the field for larger one.