A bending angle adjustment mechanism includes a rod member that is disposed along a traveling path of a long member that is connected to a bending portion that is bendable and has a threaded portion formed thereon, an adjustment piece that is disposed in a predetermined position of the rod member by being engaged with the threaded portion, and restricts movement of the long member, a head portion that is provided at an end portion of the rod member to rotate the rod member, a support member that is provided at both ends of the rod member and rotatably supports the rod member, and a convex portion that protrudes to be higher than a lower edge position of an outer circumferential edge portion of the head portion while keeping the head portion of the rod member which is supported by the support member, in a rotatable state.