An imaging optical system images a one-dimensional image on an image surface by regarding as an object a light modulator element which has light modulator parts arranged one-dimensionally in a first direction, and regarding a bundle of rays from the light modulator element as an object light. The imaging optical system includes at least two anamorphic surfaces each having radii of curvature which are different on an object surface in the first direction and a second direction which is perpendicular to the first direction, so that imaging surfaces in the first and second directions match.