Abstract: A two-group two-element lens system for use in an optical information device includes a first lens adapted to be positioned closer to a light source and having a flat surface which is symmetric with respect to an optical axis thereof and a convex surface which is symmetric with respect to the optical axis, the first lens being made of a medium having a refractive index distribution along the optical axis, and a second lens adapted to be positioned closer to an image and having a spherically convex surface closer to the light source, the second lens having a positive refracting power as a whole and made of a medium having a uniform refractive index.