A zoom lens system having at least five lens units, each lens unit being composed of at least one lens element, the zoom lens system, in order from an object side to an image side, comprising: a positive first lens unit; and a negative second lens unit, and in order from the image side to the object side, comprising: a positive lens unit γ; a negative lens unit β; and a positive lens unit α, wherein the first lens unit is composed of only optical elements having optical power, and in zooming from a wide-angle limit to a telephoto limit, at least the positive first lens unit is fixed with respect to an image surface, the positive lens unit α moves with respect to the image surface separately from an aperture diaphragm, and the negative lens unit β moves to the object side.