Disclosed is a zoom lens system including a first lens unit having a positive optical power, a second lens unit having a negative optical power, and a rear unit including at least one lens unit, which are disposed in the stated order from an object side to an image side. At least two lens units move for zooming so that a distance between adjacent lens units is changed. In this zoom lens system, the first lens unit includes a composite optical element in which a first optical element having a positive optical power and a second optical element having a negative optical power are cemented to each other. Refractive indexes and Abbe numbers of materials of the first optical element and the second optical element are set appropriately so that high optical performance is realized.