To provide a cam forming method for a zoom lens barrel with which movable ranges of respective lens groups can be sufficiently secured and the strength of a cam tube can be secured as well, without enlarging the cam tube even if a plurality of cam grooves are formed on one and the same circumferential surface of one and the same cam tube.

In the cam forming method for the zoom cam lens including a first lens group and a second lens group which perform zooming and a cam for relatively moving these lens groups, one ends of a first cam region for moving the first lens group in the direction of an optical axis and a second cam region for moving the second lens group in the direction of the optical axis are partially superposed and formed, to drive the group interval between the first lens group and the second lens group to a prescribed interval amount for zooming, over the entire area of zooming, and the deviation amount of the group interval between the first lens group and the second lens group caused by the superposed parts and the other end of the first cam region or the second cam region are corrected.