A zoom lens system including, in order from an object, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power, upon zooming from a wide-angle end state W to a telephoto end state T, varying respective distances between adjacent lens groups G1, G2, G3, G4, shifting at least one portion of the third lens group G3 in a direction including a component perpendicular to the optical axis, and satisfying given conditional expressions, thereby providing a zoom lens system having a lens capable of moving in a direction including a component perpendicular to the optical axis, and realizing a high zoom ratio and excellent optical performance.