The purpose is to provide a higher-quality three-dimensional image with a downsized optical system that does not need interpupillary adjustment. An ocular optical system according to the present disclosure includes, on an optical path viewed from an observer side, at least: a first polarization member； a mirror； a second polarization member； and an image display device in this order. A polarized state in the first polarization member and a polarized state in the second polarization member are orthogonal to each other.
