A drive mechanism includes a rotational cylinder capable of moving upon the optical axis, a cam part on a fixed member and a cam follower which is formed on the rotational cylinder fitting with the cam part and has a conical portion and a cylindrical portion. The cam part includes a tapered cam groove formed such that the cylinder extends in the optical axis upon a range whereupon the cylinder moves from the collapsed state to a photography state and a planar surface formed such that the cylinder does not move upon the optical axis upon the photography range. The conical portion fits with the cam groove of the cam part upon the range whereupon the cylinder moves upon the optical axis, and the cylindrical portion fits with the planar surface of the cam part upon the range whereupon the cylinder does not move upon the optical axis.