A holding mechanism includes an opening portion through which the guide member is inserted in a bending state. The mechanism includes a gap portion which has a cutout surface that is provided by cutting out one part of the holding mechanism in a radial direction of a central axis of an insertion opening portion, and that guides the guide member into the opening portion from the insertion opening portion. The mechanism includes a lock mechanism which is provided in the radial direction and which locks the guide member inserted through the opening portion at two places different from each other in positions in the central axis direction of the insertion opening portion so that one part of the guide member maintains the bending state.
