FIG. 28B is a plan view showing the inner side surface of the upper second housing portion 102 b shown in FIG. 28A. FIG. 28C is a plan view showing an outer side surface of the upper second housing portion 102 b shown in FIG. 28A. Referring to FIGS. 28A, 28B and 28C, the conductor layer 102 bm made of an electrically conductive material such as magnesium or zinc and including an inverted-U-shaped