A portable information device case according to the present invention includes three plate-like members: a holder part for housing a portable information device (smartphone) therein, a cover part for covering the holder part, and an optical panel part including an image-forming optical element (micromirror array) fitted therein in light-transmissive fashion. When these members are combined together to have a predetermined shape, the optical panel part is held in an attitude inclined at a predetermined angle with respect to a display surface of the smartphone. Thus, the case allows selection with ease between a usage form in which an image appearing on the display surface is projected as a spatial image and a storage form in which these members are folded and stacked so that the entire case is made compact. The portable information device case according to the present invention is easy to carry.