A zoom lens is disclosed. An optical system consists, sequentially along a light incident direction, of a first lens group A having a negative focal power, a second lens group B having a positive focal power, a diaphragm S, a third lens group C having a negative focal power and a fourth lens group D with a positive focal power. The first lens group A and the third lens group C are always in a fixed state. The second lens group B is moved from an image side to an object side along the optical axis so that the lens field angle is zoomed from a wide-angle end to a telephoto end. At the same time, the fourth lens group D is moved correspondingly in a non-linear manner along the optical axis for correction and focusing with the image variation accompanying the zooming. The stability of the system image during the variation in the focal length is ensured.