PURPOSE: To reduce lens extension torque by pivotally supporting tow cam followers to be engaged with a guide hole of a lens guiding cylinder and a can hole of a cam cylinder with a supporting shaft of a lens frame.

CONSTITUTION: The lens frame 17 having a lens 20 on the inside of the guide cylinder 15 having the guide hole 16 is slided in the optical axis direction and the cam cylinder 24 having the cam hole 25 is arranged on the outside of the cylinder 15. The cam followers 26, 27 are pivotally contacted with the sides of the holes 16, 25 respectively and a screw 28 for coupling the followers 26, 27 is engaged with a screw hole 19 of the frame 17. When the cylinder 24 is rotated from the guide cylinder 15 in the E direction, the cam follower 27 is pressed in the circumferential direction and component force in the optical axis F direction is obtained. Since the followers 26, 27 are independently rotated, frictional force can be reduced and the lens can be easily extended in the optical axis F direction, so that the extension torque of the lens can be reduced.