To provide a display device in which the brightness of the image viewed by the observer is bright, and the brightness of the image is as uniform as possible. The display device according to the present invention includes a frame 10 and an image display device 100, the image display device 100 includes an image forming apparatus 11 and an optical device 120, the optical device 120 includes a light guide plate 121, a first deflection unit 130 configured with a first hologram diffraction grating 131 and a second hologram diffraction grating 135, and a second deflection unit 140 configured with a third hologram diffraction grating 141, and slant angles and pitches of the first hologram diffraction grating 131, the second hologram diffraction grating 135, and the third hologram diffraction grating 141 satisfy a predetermined relation.