A zoom lens system is composed of negative, positive, negative, and positive lens groups, of which at least the first to third move during zooming. During zooming from the wide-angle end to the telephoto end, the distance between the first and second lens groups decreases, the distance between the second and third lens groups varies, and the distance between the third and fourth lens groups increases. The conditional formulae 1.0≦|f2/f1|≦1.5 and 2.0≦|f4/f1|≦5.0 are fulfilled (f1, f2, and f4 representing the focal lengths of the first, second, and fourth lens groups).