Each of a plurality of Fresnel prisms 12 is formed so that a refractive surface 12 thereof includes a non-light incidence surface 12c upon which any light ray emitted from a projector 1 is not directly incident because it is intercepted by another Fresnel prism 12, the non-light incidence surface having an angle .tau.' with a reflective surface 12b which is different from the prism apex angle .tau. of each of the plurality of Fresnel prisms. As a result, a light ray reflected by the refractive surface 12a of each of the plurality of Fresnel prisms without passing through the refractive surface can be preventing from emerging, as unnecessary light, toward the viewer's line of sight.