An endoscope comprising: a manipulation unit; and an insertion unit that is disposed in continuation to the manipulation unit and that includes a bending portion, wherein the insertion unit comprises in the bending portion: a plurality of articulation wheels coupled in succession; and a plurality of shaft members, each shaft member including a guide part formed with an insertional hole through which a wire is inserted, wherein four wires are laid along the center axis of the bending portion; wherein two adjacent ones (21a,21b) of the plurality of articulation wheels are coupled by shaft members so as to be relatively turnable around the shaft members on a direction crossing a center axis of the bending portion, the bending portion is bent in such a way that the wire which leads to the manipulation unit via the plurality of articulation wheels is tractively manipulated, each guide part of the shaft members is turnable around a center axis of each shaft member, to both of the two articulation wheels (21a,21b) which are coupled by two shaft members, wherein each plurality of articulation wheels has a coupling part (22a, 22b) formed with a shaft hole (23a, 23b) through which the shaft member is inserted, the two adjacent articulation wheels are coupled in such a way that the shaft member (31, 41, 51) is inserted through the shaft holes (23a, 23b) of the respective coupling parts which are placed one over the other, characterized in that each shaft member further includes a secured part, wherein the guide part and the secured part of each shaft member are separate components that are connected to each other, and wherein the secured parts are secured to either of the two coupling parts (22a, 22b) placed one over the other, characterized in that the guide part is provided with a spherical joint, and the secured part comprises a socket, wherein, for each shaft member, the socket of the respective secured part accommodates the spherical joint of the corresponding guide part, such that the guide part is turnable around the center axis of the secured part. a manipulation unit; and an insertion unit that is disposed in continuation to the manipulation unit and that includes a bending portion, wherein the insertion unit comprises in the bending portion: a plurality of articulation wheels coupled in succession; and a plurality of shaft members, each shaft member including a guide part formed with an insertional hole through which a wire is inserted, wherein four wires are laid along the center axis of the bending portion; a plurality of articulation wheels coupled in succession; and a plurality of shaft members, each shaft member including a guide part formed with an insertional hole through which a wire is inserted, wherein four wires are laid along the center axis of the bending portion; wherein two adjacent ones (21a,21b) of the plurality of articulation wheels are coupled by shaft members so as to be relatively turnable around the shaft members on a direction crossing a center axis of the bending portion, the bending portion is bent in such a way that the wire which leads to the manipulation unit via the plurality of articulation wheels is tractively manipulated, each guide part of the shaft members is turnable around a center axis of each shaft member, to both of the two articulation wheels (21a,21b) which are coupled by two shaft members, wherein each plurality of articulation wheels has a coupling part (22a, 22b) formed with a shaft hole (23a, 23b) through which the shaft member is inserted, each shaft member further includes a secured part, wherein the guide part and the secured part of each shaft member are separate components that are connected to each other, and wherein the secured parts are secured to either of the two coupling parts (22a, 22b) placed one over the other,