A lens barrel capable of keeping a stable zoom operation, increasing magnification of an image pickup apparatus with a simple configuration, and decreasing a camera thickness. A lens barrel is moved in an optical axis direction between a taking position and a retracted position to change magnification. A lens holding member holds a lens and has a follower part. A rectilinear movement regulating member regulates relative rotation of the lens holding member and has a convex part at an outside and a rectilinear rib at an image surface side than the convex part. A cam barrel has a cam groove for engaging the follower part and a groove for engaging the convex part formed on an inner surface. The cam barrel has a cam piece extended to the image surface side, a part of the cam groove is formed on an inner surface of the cam piece.