A simple, compact, high-zoom-ratio zoom lens system exhibiting high optical performance at all zoom positions is provided. The system includes, in order from the object side to the image side, first to fourth lens groups having positive, negative, positive, and positive refractive powers, respectively. The first-to-second-lens-group distance becomes the smallest during zooming. The first lens group resides closer to the object at a telephoto end than at a wide-angle end. The lens groups move such that the second-to-third-lens-group distance is smaller and the third-to-fourth-lens-group distance is larger at the telephoto end than at the wide-angle end. The second lens group includes, in order from the object side to the image side, negative and positive lens elements. First-to-second-lens-group distances d1w and d1t at the wide-angle end and at the telephoto end, respectively, and the smallest first-to-second-lens-group distance d1min obtained during zooming are appropriately set.