To obtain a modified Gauss type lens in which high reading density is realized when it is used near the image forming magnification of 0.16535 and a sufficiently large viewing angle and sufficient brightness can be obtained.

A 1st group is constituted of a 1st positive meniscus lens of which the surface on an object side is convex. A 2nd group is constituted by combining a 2nd positive meniscus lens whose the surface on the object side is convex and a 3rd negative meniscus lens whose surface on an image side is concave. A 3rd group is constituted by combining a 4th negative meniscus lens whose the surface on the object side is concave and a 5th positive meniscus lens whose surface on the image side is convex. A 4th group is constituted of a 6th positive meniscus lens of which the surface on the image side is convex. A 5th group is constituted of a 7th positive meniscus lens whose surface on the image side is convex. Then, when the focal distances of the 4th and the 5th groups are defined as (f4) and (f5), the refractive indexes of the 2nd and the 3rd lenses are defined as (n2) and (n3), the Abbe's numbers of the 2nd and the 3rd lenses are defined as ν2 and ν3 and the radiuses of the curvature of surfaces obtained by counting the surfaces from the object side are defined as R3, R4 and R5, the respective conditions of 0.60<f4/f5<1.50, -0.250<n2-n3<-0.100, 25.0<ν2-ν3<45.0 and 0.70<(R3+R5)/R4<1.30 are satisfied.