To provide a projection optical system capable of projecting picture information displayed on a liquid crystal display element or the like on a screen surface while maintaining high optical performance though it has excellent telecentricity and long back focus.

A projection lens system for projecting the picture information on the display element to a specified surface is constituted of a 1st lens group (G1) having negative refractive power and a 2nd lens group (G2) having positive refractive power in order from a screen side. The optical system satisfies fB/f>2.5 and 2.0<fII/f<2.8. It is desirable to use a glass material satisfying (θ-0.535)/(ν-65)>0 in order to correct chromatic aberration of magnification for at least one of negative lenses in the 1st lens group or at least one of positive lenses in the 2nd lens group. Also, a glass material satisfying nd>1.75 and νd<28 is used. Furthermore, the 1st and the 2nd lens groups (G1 and G2) respectively include at least one aspherical lens.