Magnetic domain structures of finely crystallized Fe_73.5Cu₁Nb₃Si_13.5B₉ alloys have been studied by Lorentz microscopy. We found the size of the uniform area (d_u) having a locally uniform anisotropy strongly affects the domain structure and the associated magnetic properties. In the highest-permeability alloy annealed at 550°C, circularly magnetized domain patterns were observed. Since the domain-wall width (w_d) is about five times as large as the area having a magnetic uniform anisotropy for the highest-permeability alloy (w_d∼5d_u), effects of the anisotropy field are averaged to zero, resulting in free movement of the domain wall.