Endoscope

1. An endoscope comprising:

an insertion portion that is inserted into a subject;

a bendable first bending portion that is provided on a distal end side of the insertion portion;

a bendable second bending portion that is provided in the insertion portion closer to a proximal end side than the first bending portion;

a bending operation wire that is inserted into the insertion portion, a distal end of the bending operation wire being fixed to the first bending portion;

a first coil sheath that is inserted into the second bending portion, the bending operation wire being inserted thereinto so as to be freely movable in a longitudinal direction of the insertion portion and a distal end of the first coil sheath being fixed to a distal end side of the second bending portion;

a switching mechanism that switches between fixing and unfixing of a proximal end of the first coil sheath and moves the proximal end of the first coil sheath in the longitudinal direction inside the insertion portion when the proximal end of the first coil sheath is unfixed;

a guide section that is fixed to an inner surface of the second bending portion, comprising a through hole that the first coil sheath penetrates in the longitudinal direction, and holding the first coil sheath penetrating the through hole so that the first coil sheath runs along the inner surface of the second bending portion;

a first region that is formed into a curved surface on an inner surface on a distal end side of the guide section;

a second region that is formed into a curved surface on an inner surface on a proximal end side of the guide section; and

a central part that is formed between the first region and the second region on the inner surface of the guide section, has a shape protruding toward a center of the through hole of the guide section relative to the first region and the second region and is formed to have a length in the longitudinal direction longer than a diameter of a wire making up the first coil sheath.

2. The endoscope according to claim 1 ,

wherein the inner surface of the guide section is formed into a shape in which a diameter of the through hole decreases from the distal end and the proximal end of the guide section in the longitudinal direction toward the central part.

3. The endoscope according to claim 2 ,

wherein the central part of the inner surface has a predetermined length along the longitudinal direction and the diameter of the through hole of the central part is constant along the longitudinal direction, and

a region that connects the distal end and the proximal end of the guide section on the inner surface and the central part is formed into a curved surface and a radius of curvature of the curved surface is smaller than a bending radius of the first coil sheath that passes through the through hole when the second bending portion is bent at a maximum bending angle.

4. The endoscope according to claim 2 ,

wherein the inner surface of the guide section is formed into a curved surface, and

a radius of curvature of the inner surface is smaller than a bending radius of the first coil sheath that passes through the through hole when the second bending portion is bent at a maximum bending angle.

5. The endoscope according to claim 2 , further comprising:

bending pieces provided in the second bending portion and connected together along the longitudinal direction to bend the second bending portion; and

a groove provided in an inner surface of the bending piece, part of the guide section being fitted into the groove in a region to which the guide section is fixed.

6. The endoscope according to claim 2 , further comprising bending pieces provided in the second bending portion, the bending pieces being connected together along the longitudinal direction to bend the second bending portion,

wherein the guide section is fixed on the inner surface of the bending pieces at a position where the guide section does not protrude from a line connecting a rotating shaft provided at a distal end of the bending piece in the longitudinal direction and the distal end of an outer circumferential face of the bending piece, toward the distal end of the insertion portion.

7. The endoscope according to claim 1 , further comprising bending pieces provided in the second bending portion, the bending pieces being connected together along the longitudinal direction to bend the second bending portion,

wherein part of a perimeter of the bending piece is folded in a concave shape inside in a diameter direction of the bending piece so that the guide section has the through hole and is formed integrally with the bending piece.

8. The endoscope according to claim 1 , wherein the inner surface of the guide section is subjected to friction-reducing treatment to reduce friction with the first coil sheath contacting the inner surface.