A zoom lens system with a new structure is disclosed which realizes high optical performance by appropriately setting the structure of each lens unit and using a material with anomalous dispersion in an appropriate lens unit. Specifically, according to several aspect herein disclosed, the zoom lens system includes, in order from an object side to an image side, lens units having a positive, a negative, and a positive optical powers in which the structure of each lens unit is specified or a third lens unit employs a lens element made of a material with anomalous dispersion.