A zoom lens system having a wide field angle, a long back focal length, a high zooming ratio, and comprising a small number of lens elements. Said zoom lens system comprises, in the order from the object side, a front lens unit having negative refractive power and a rear lens unit having positive refractive power, and is so adapted as to perform variation of focal length, said front lens unit consisting of a negative meniscus lens element having a convex surface on the object side, a negative lens element and a positive lens element, whereas said rear lens unit comprising, on the extremely image side therein, a positive lens component consisting of a positive lens element having a short radius of curvature on the image side surface thereof and a positive lens element having a short radius of curvature on the object side surface thereof.