A holding mechanism includes a first guide portion which contacts and guides part of a guide member in a state where the guide member exposed from an insertion opening portion of the insertion device is bent, and a second guide portion which permits passage of the part of the guide member which has been guided by the first guide portion. The holding mechanism also includes a regulating/fixing portion which is arranged parallel to a flat face where an insertion opening portion is provided, which is continuous with the second guide portion, and which positions and fixes the part such that the guide member including the part having passed the second guide portion maintains a bent state with respect to the insertion opening portion.