Providing a zoom lens system being compact with high optical performance, an optical apparatus using the same, and a method for zooming the zoom lens system. The system includes, in order from an object along an optical axis, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. Upon zooming from a wide-angle end state W to a telephoto end state T, each distance between adjacent lens groups is varied. Given conditional expression is satisfied.