An optical sheet has an isotropic medium layer and an anisotropic medium layer. The isotropic medium layer is made of an optically isotropic medium and has a first surface and ridge-shaped projections. The projections are formed on the first surface, arranged in a first direction and extend in a second direction intersecting at right angles to the first direction. Each projection has a cross section shaped like a segment of a circle. The anisotropic medium layer is made of an optically uniaxial medium and has a second surface and groove-shaped recesses. The recesses are made in the second surface, arranged in the first direction and extend in the second direction. Each recesses has a cross section shaped like a segment of a circle. The isotropic and the anisotropic medium layers are laid one on the other, with the respective projections firmly fitted in the respective recesses.