To obtain a compact high-performance zoom lens system for a digital still camera or a video camera, whose zoom ratio is about 3.6.

This zoom lens system is constituted of four lens groups, that is, positive, negative, positive and positive lens groups in order from an object side. In the case of zooming from a wide end to a telephoto end, at least 1st, 2nd and 3rd lens groups move so that space between the 1st and the 2nd lens groups may be increased, space between the 2nd and the 3rd lens groups may be decreased and space between the 3rd and the 4th lens groups may be increased. The zoom lens system satisfies following conditional expressions (1) to (3). (1) 0.10<fw/f1<0.30 (2) 0.25<fw/f4<0.45 and (3) 0.60<X3/(ft-fw)<0.85 Provided that (fw) means the focal distance of an entire system at the wide end, (ft) means the focal distance of the entire system at the telephoto end, (fi) means the focal distance of an i-th lens group (i=1 to 4), X3 means the moving quantity of the 3rd lens group from the wide end to the telephoto end, and (f) means the focal distance of the entire system.