A high-ratio zoom lens system includes a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group, in that order from the object. Upon zooming from the short focal length extremity to the long focal length extremity, the first through fourth lens groups move along the optical axis of the zoom lens system while increasing the distance between the first and second lens groups, and decreasing the distance between the second and third lens groups. The following conditions are satisfied: 0.9