Abstract: An illumination device for a direct viewing type display element comprising a flat light guide; a light source set such that light is incident on a side portion of said flat light guide; a polarized light separating flat set on a first side of a light emitting side of the flat light guide for transmitting a p polarized light component and reflecting at least a portion of an a polarized light component with respect to a light ray substantially having a predetermined direction of incidence; and a light reflecting sheet disposed on a second side opposite to said light emitting side of the flat light guide in parallel with the light emitting site.