PURPOSE: To obtain a zoom lens having a wide angle and a high variable power ratio by satisfying a prescribed condition in a lens system consisting of three groups which are arranged in order from the object side and have positive, negative, and positive refractive indexes respectively.

CONSTITUTION: The lens system consists of a first lens group I, a second lens group II, and a third lens group III in order from the object side. The third lens group III is divided into a front group III-F and a rear group III-B; and in case of zooming from the wide angle end to the telephoto end, the first group I and the rear group III-B of the third group are moved to the object side to change intervals between the first and the second groups, between the second and the third groups, and between the front group and the rear group of the third group. The condition of βF<-1 and the condition of a formula where βF, fW, TIII-B, and BW are the lateral magnification of the third group III at an optional focal length, the focal length of the whole of the system in the wide angle end, the thickness on the axis of the rear group III-B of the third group, and the back focus in the wide angle end respectively are satisfied so that the front group III-F and the rear group III-B of the third group are moved to the image side in all of the focal length area to focus the lens system on an object point at a short distance.