A zoom optical system in which: a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group are arranged in that order from the object side and magnification is changed by properly changing distances between these lens groups; the first lens group consists of only one lens element and the most object-side surface of the first lens group has a convex shape which faces toward the object side; the second lens group includes, in order from the object side, a negative single lens, a negative cemented lens, and a positive single lens; and the following condition (1) or (2) is satisfied: 0.2≦ΔDw-w10/Lt≦0.35  (1) SFG4=(rG4o+rG4i)/(rG4o−rG4i)>0  (2) where ΔDw-w10 denotes the variation in the distance between the first and second lens groups in changing from the wide angle end position to the position in which the focal length is ten times or more as large as that in the wide angle end position, Lt denotes the total length of the optical system in the telephoto end position, SFG4 denotes the shape factor of the fourth lens group, rG40 denotes the radius of curvature of the most object-side surface of the fourth lens group, and rG4i denotes the radius of curvature of the most image-side surface of the fourth lens group.