A zoom lens system comprising a first lens unit having negative power, a second lens unit having positive power and a third lens unit having positive power, wherein: the first lens unit comprises a first lens element having a concave surface at least on the image side and negative power and a second lens element having a convex surface at least on the object side and positive power; the second lens unit comprises a first cemented lens element of two lens elements having power of mutually different signs and a second cemented lens element of two lens elements having power of mutually different signs; in zooming, all of the lens units move along an optical axis; and conditions (1): 5.0<.alpha.i.sub.W<20.0 and (I-2): n.sub.11.gtoreq.1.9 (where, 3.235, .alpha.i.sub.W is an incident angle of a principal ray to an image sensor at a maximum image height at a wide-angle limit, n.sub.11 is a refractive index of the first lens element to the d-line, .omega..sub.w is a half view angle at a wide-angle limit, and f.sub.T and f.sub.W are focal lengths of the entire system at a telephoto limit and a wide-angle limit, respectively) are satisfied.