A zoom lens system comprising a positive first lens unit, a positive second lens unit, and at least two subsequent lens units, wherein the first lens unit moves along an optical axis at the time of zooming, an interval between the second lens unit and one of the at least two subsequent lens units varies at the time of zooming or focusing, the first lens unit is composed of at least three lens elements, each of the first lens unit and the second lens unit includes at least one negative lens element, and the conditions: 0.008