A polarization split device that includes an optically isotropic substrate, an optically anisotropic film, and a diffraction grating. The optically anisotropic film is formed on the optically isotropic substrate. The diffraction grating includes first and second cyclically structural portions. The first cyclically structural portion is formed on a front surface of the optically anisotropic film such that a depression in a rectangular shape is cyclically arranged with a predetermined pitch. The second cyclically structural portion includes an optically transparent material having a refractive index approximately equivalent to a refractive index of the optically anisotropic film and is configured to cover the first cyclically structural portion. Diffraction light having a diffraction angle greater than a predetermined angle among diffraction light diffracted by the diffraction grating is inhibited from being discharged outside.