PURPOSE: To well correct various aberrations and more particularly chromatic aberrations and to obtain optical performance high over the entire part of object distances by adequately setting the lens constitution and glass materials of respective lenses.

CONSTITUTION: This Gauss type lens consists of the lens constitution of 6 elements in four groups consisting, successively from an object side, of the combined lens GA of a negative refracting power as a whole formed by joining the first lens G1 of a positive refracting power, the convex face of which is directed to the object side, the second lens G2 of the positive refracting power, the convex face of which is directed to the object side, and the third lens of the negative refracting power, the concave face of which is directed to the image plane side, a stop SP, a combined lens GB of the negative refracting power as a whole formed by joining the fourth lens G4 of the negative refracting power, the concave face of which is directed to the object side, and the fifth lens G5 of the positive refracting power, the convex face of which is directed to the image plane side, and the sixth lens G6 of the positive refracting power, the convex face of which is directed to the image plane side. The conditions 1.64<Nd<1.66, 37<νd<39.0, 0.59<Pg, F<0.61 are satisfied when the refractive index, Abbe number and partial dispersion ratio of the material of the one lens among the first, second, fifth and sixth lenses are defined respectively as Nd, νd, Pg,F.