Object is to provide an inner-focusing type zoom lens system carrying out
focusing by moving a portion of a first lens group suitable for an
auto-focus SLR camera. A zoom lens system includes, in order from an
object, a first lens group having positive refractive power, a second
lens group having negative refractive power, and a third lens group
having positive refractive power. Upon zooming from a wide-angle end
state to a telephoto end state, a distance between the first and the
second lens groups increases, and a distance between the second and the
third lens groups decreases. The first lens group is composed of, in
order from the object, a 1A lens group G1A having positive refractive
power, and a 1B lens group G1B having positive refractive power. Focusing
from infinity to a close-range object is carried out by moving only the
1B lens group G1B to the object.