A positive first lens group G1, a negative second lens group G2, an aperture diaphragm St, a positive third lens group G3, and a positive fourth lens group G4 are sequentially arranged, and a movement of the lens groups and the aperture diaphragm St during zooming is optimized in combination with an appropriate conditional expression. During zooming, a position of the aperture diaphragm St on an optical axis at a wide-angle end is closer to an image plane than that at a telephoto end, and a space on the optical axis at the wide-angle end between the aperture diaphragm St and the third lens group G3 is larger than that at the telephoto end, thereby suppressing the length of the whole lens. Also, heights of rays passing through the first lens group G1 are lowered, thereby suppressing the lens diameter of the first lens group G1. The following conditional expression is satisfied: 0.4<(Pt-Pw) / fw<0.9 (1), where fw denotes a focal length of the whole system at the wide-angle end, Pw denotes a distance on the optical axis at the wide-angle end between the image plane and the stop, and Pt denotes a distance on the optical axis at the telephoto end between the image plane and the stop, thereby realizing a high variable power ratio and a small size as a whole.