A step-zoom lens includes two movable lens groups; a lens group support unit; and a cam ring having a cam groove. The cam groove includes a finite number of focal-length steps, so as to perform a focusing operation between infinite and closest photographing positions at each focal-length step. The cam groove includes a wide-angle mode section, a telephoto mode section, and a mode switching section. The closest photographing positions in two adjacent focal-length steps and the infinite photographing positions in two adjacent focal-length steps are adjacent to each other, respectively. One focal-length step of the infinite photographing position at a longest focal length in the wide-angle mode section is provided at one end of the mode switching section, and another focal-length step of the infinite photographing position at a shortest focal length in the telephoto mode section is provided at the other end.