PURPOSE: To improve the operability of the switching of a focusing speed with simple structure by forming the 2nd lead part differing in lead from the 1st lead part successively to the 1st lead part and forming an endless inner cam groove.
CONSTITUTION: When a cam cylinder 4 is rotated relatively to a fixed cylinder 1, a moving ring 2 moves in an optical-axis direction through a pin 2a according to the cam groove 4a to focus a photographic lens 3. When a stationary subject is photographed normally, the moving ring 2 jogs by using a small-lead part A of the cam groove 4a, so the focusing is performed with high precision. Further, when a dynamic subject is photographed, the focusing is performed speedily by using a large-lead part C of the cam groove 4a. The switching from the part A to the part C of the cam groove 4a or reverse switching is performed continuously, smoothly, and easily by passing the moving ring through a zerolead part B or D by the rotation of the cam cylinder 4 in the same direction.