According to one embodiment, a display device includes an illumination device, a display panel, a first polarizer attached to the display panel, a second polarizer attached to the display panel, and a transmissive diffraction grating provided in a location between the illumination device and the first polarizer or in a location facing the second polarizer. The diffraction grating includes a third substrate, a fourth substrate, and a second liquid crystal layer provided between the third substrate and the fourth substrate, containing a plurality of liquid crystal molecules, and cured in a state where alignment directions of the liquid crystal molecules are fixed.