Abstract: This specification discloses an f.theta. lens system having an entrance pupil at a remote position on the incident light side of the lens system and having such a negative distortion that the image height H of a parallel light beam incident at an angle .theta. with respect to the optical axis with the entrance pupil as the center is H=f.theta., where f is the focal length of the entire system. The lens system includes, in succession from the entrance pupil side, a first group having at least one negative lens and having a composite negative refractive power, a second and a third group each having a meniscus lens component having its concave surface facing the entrance pupil side, and a fourth group having at least one positive lens and having a composite positive refractive power.