There is provided a collapsible lens barrel including plural barrels of different outside diameters from one another and enabled to move coaxially and perform relative movement in an axial direction, and an image-capturing optical system disposed within the plural barrels; wherein the image-capturing optical system includes at least two lens holding frames arranged in a direction of an optical axis of the image-capturing optical system; and, considering an object side is set as a front side and an opposite side is set as a rear side, each of a rearmost lens holding frame, placed at a rearmost position, and one of the lens holding frames placed immediately in front of the rearmost lens holding frame, are respectively movably supported by a corresponding guide mechanism to move in the direction of the optical axis and to move in the direction of the optical axis by a corresponding drive mechanism.