in the embodiment; [0025]FIG. 7A and FIG. 7B are a front view and a side view showing a third example of the structure for resiliently supporting the optical sheets on the frame member, employed in the embodiment; [0026]FIG. 8A and FIG. 8B are a front view and a side view showing a variant of the third example shown in FIG. 7; [0027]FIG. 9A and FIG. 9B are a front view and a side view showing a f