There is provided an optical device including a display device, and a transparent substrate that is disposed on a side of a display surface of the display device. When the transparent substrate is evaluated by using a three index values of a resolution index value T, a reflection image diffusiveness index value R, and a sparkle index value S, the following conditions are satisfied: the resolution index value T≤0.2, the reflection image diffusiveness index value R≥0.2, and the sparkle index value S≤60.