PURPOSE: To obtain a zoom lens which is used at about 3 times to 10 times variable power rate, is long in back focus and has excellent imaging performance by using a first lens group which has three elements of negative lenses and satisfies specific conditional equations.

CONSTITUTION: This zoom lens is formed, successively from an magnifying side (printing paper side), the first lens group L1 having negative refracting power, a second lens group L2 having positive refracting power, a third lens group L3 having negative refracting power and a fourth lens group L4 having positive refracting power. The specified distance between the object images at which the first lens group L1, the second lens group L2, the third lens group L3 and the fourth lens group L4 move to the magnifying side is obtd. at the time of varying power from a short focal length to a long focal length. Further, the first lens group L1 has at least three elements of the negative lenses and satisfies the conditions of equation I, equation II. In the equations I, II, fw denotes the focal length of the entire system on the short focal side; f1 denotes the combined focal length of the first lens group L1; ν denotes the average value of the Abbe number of the negative lenses of the first lens group L1.