A zoom lens system comprises, from an object side to an image side: a first lens unit; a second lens unit; a third lens unit; a fourth lens unit; and a fifth lens unit having positive refractive power, wherein: in zooming from a wide angle end to a telephoto end, the first, the second, the third, and the fourth lens units move so that an interval between the first and the second lens units is larger at the telephoto end than that at the wide angle end, an interval between the second and the third lens units is smaller at the telephoto end than that at the wide angle end, and a distance between the third and the fourth lens units varies; and a focal length of the first lens unit, and focal lengths of an entire system at the wide angle end and the telephoto end are appropriately set.