An optical device according to an embodiment of the present disclosure includes a light source in which a plurality of light emitting elements are arranged at a predetermined distance, an optical system configured to convert light beams from the plurality of light emitting elements into line light beams, and a light deflection element configured to deflect each of the line light beams. Each of the line light beams is caused to be incident on the light deflection element such that a longitudinal direction of each of the light beams is aligned with a direction of a rotating axis of the light deflection element.