An optical device displaying an image of a blind spot includes a blind spot-side outward mirror disposed on a blind spot-side of a line of sight with respect to an obstacle; a blind spot-side inward mirror disposed to face the blind spot-side outward minor; an eye point-side inward mirror disposed on an eye point-side of the line of sight with respect to the obstacle; and an eye point-side outward minor disposed to face the eye point-side inward mirror. Each of the blind spot-side inward mirror and the eye point-side inward mirror has a plurality of reflection surfaces, and the reflection surfaces are arranged in parallel with each other and arranged at positions where the reflection surfaces partially overlap with each other.