A zoom lens system includes, in order from an object side to an image side, a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power, and a fourth lens unit having positive optical power. Each lens unit moves during zooming. In particular, the first lens unit moves so as to be closer to an object at a telephoto end than at a wide-angle end during zooming, and the fourth lens unit moves in a locus convex toward the object side during zooming. The sharing of magnification variation between the third lens unit and the fourth lens unit is appropriately set.