An optical system includes a light source, an illumination optical system, and an optical modulator. The lens array and the lens of the illumination optical system are arranged in that order from an upstream side of an optical path of light from the light source. The light shield is disposed at the upstream side relative to the lens in the optical path. The light shield blocks some rays incident within a range of an effective diameter of the lens. The illumination optical system emits the light to the optical modulator. The optical modulator emits the incident light to a first direction and a second direction different from the first direction. A center of an effective diameter of the lens array is offset from a center of the effective diameter of the lens to an opposite side of the light shield in a direction orthogonal to the optical axis.