The invention is directed to inner-focusing zoom lenses that include multi groups of lens pieces, namely, the first lens group or the leading lens group of positive refractivity, the second lens group of negative refractivity, and the remaining trailing groups of positive refractivity, as a whole. At least one group of positive refractivity among the trailing groups includes two or more negative lens pieces, at least one of which is connected on its surface to another lens piece to form a duplicated composite lens so that the junction between two of them functions to diverge incident beams. Assuming now that a sum of the refractivities of all the junctions of the composite lenses can be expressed as Σφ=Σ|(N1−N2)/R| where N1 and N2 are refractivities that substances before and after the junction of the composite lenses respectively have, R is a radius of curvature of the junction, ft is a focal length of the comprehensive lens optics of the zoom lens at the telephoto end.