ZOOM LENS UNIT

PROBLEM TO BE SOLVED: To provide a zoom lens unit having a focusing group lens system with a reduced weight, which reduces a load on a focus drive system, and an anti-shake lens system having a smaller diameter and reduced weight, which reduces a load on an anti-shake drive system and allows for reducing size of the anti-shake drive system.SOLUTION: A zoom lens unit comprises, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power, and a fifth lens group having positive or negative refractive power. Focusing is accomplished by the fourth lens group alone. The third lens group and the fifth lens group move along a same cam track when zooming. When zooming from the wide-angle end to the telephoto end, a distance between each pair of adjacent lens groups changes. Some of the lens groups function as an anti-shake lens group. A partial lens group having positive refractive power is located on the object side of the anti-shake lens group with an air gap which does not change while zooming in between.