To constitute a lens system with a small number of lenses and to suppress variation in lightness between the center part and peripheral part of an image plane at the time of application to a camera equipped with a solid image pickup element.

This system consists of a stop S, a 1st lens G1 with negative refracting power, and a 2nd lens G2 with positive refracting power. The ratio of the incidence height PRL and maximum image height of lower rays of the most off-axis light beam flux in merdional section to a 2nd lens G2 and the ratio of the focal length of the 2nd lens G2 and the focal length of the whole system are adequately set.