In a display device, an image having an aspect not equal to 1 is formed by an image forming unit configured to form an image, and the image is guided as an image light to a display position by an optical system. The optical system, which is provided with a diffraction optical element, deflects the image light. In the diffraction optical element, a pitch direction of a pattern for deflecting the image light coincides with a direction in which the aspect of the image is narrow. In the display device, the direction in which the image light is deflected by the diffraction optical element coincides with the direction in which the aspect of the image formed is narrow, thus making it possible to suppress unevenness of brightness and hue within a plane of an image displayed.