A zoom lens system includes a positive first lens group, a positive second lens group, a diaphragm, and a negative third lens group. The first through third lens groups move in an optical axis direction for zooming. The positive first lens group includes a negative lens element, and at least one positive lens element. The negative lens element is positioned at the most object-side of the positive first lens group, and is provided with a concave surface on the object-side surface thereof. The zoom lens system satisfies a number of specified conditions.