A zoom lens system includes a front lens group and a rear lens group arranged from an object side to an image side in that order. The front lens group includes a plurality of lens units, and during zooming from a wide angle end to a telephoto end, imaging magnification is increased by changing spaces between the plurality of lens units. The rear lens group with positive optical power as a whole includes a lens unit IS with negative optical power being movable so as to have a direction perpendicular to an optical axis, and a lens component RB2 with positive optical power disposed on the image side with respect to the lens unit IS. A space between the lens unit IS and the lens component RB2 is changed during zooming. The following condition is established to satisfy: 0.05<|fis|/ft<0.25, wherein (fis) denotes a focal distance of the lens unit IS, and (ft) denotes a focal distance at the telephoto end of the zooming lens system.