A first frame section (11) is hollow and has a substantially uniform polygonal cross-sectional shape. An axial load is applied to the first frame section. A second frame section (13) is hollow and has a substantially uniform polygonal cross-sectional shape. The axial load is transmitted from the first frame section (11) to the second frame section (13). A transmitting portion (17) is provided in at least one of the first and second frame sections. The transmitting portion (17) receives the axial load that acts on each edge of the first frame section and transmits the axial load to each edge of the second frame section. <IMAGE>
