The present invention is a variable power zoom lens that is suitable to APS-format single-lens reflex cameras. The zoom lens has the foremost or first lens group G1 of positive refractivity, the second lens group G2 of negative refractivity, the third lens group G3 of positive refractivity, and the fourth lens group G4 of positive refractivity disposed in sequence from a position closer to the object to photograph toward the image plane. The third lens group G3 has a front lens subset G3F of positive refractivity and a back lens subset G3B, and the back lens subset G3B alone is moved orthogonal to the optical axis to correct a blur of an image on the image plane caused by a shake of photographer's hands.