A bending mechanism (100; 100A; 100B; 100C) comprising: a shaft part; a bendable part (2; 2A) whose proximal end is linked to a distal end of the shaft part, the bendable part (2; 2A) being bendable in a direction orthogonal to an axis of the shaft part; a forward end part whose proximal end is linked to the bendable part (2; 2A); an operating rod, or an operating wire, inserted through a groove or a hole of the shaft part and a groove or a hole of the bendable part (2; 2A), the groove or the hole of the shaft part being provided in a manner to extend along an axial direction of the shaft part, the groove or the hole of the bendable part (2; 2A) being provided in a manner to extend along an axial direction of the bendable part (2; 2A), the operating rod or the operating wire having a distal end thereof fixed to the bendable part (2; 2A); and a pressing portion configured to be able to press the operating rod or the operating wire against a fixed portion of the shaft part, wherein the bendable part (2; 2A) is configured to be bendable as a result of the operating rod or the operating wire being operated in an extending direction of the operating rod or the operating wire, and the operating rod or the operating wire is configured such that, when the operating rod or the operating wire is pressed against the fixed portion of the shaft part by the pressing portion, friction force is generated, and at a pressing position where the operating rod or the operating wire is pressed against the fixed portion of the shaft part, the operating rod or the operating wire is fixed in the axial direction by the friction force; characterized in that: the pressing portion includes a tube that is inserted through the groove or the hole of the shaft part adjacently to the operating rod or the operating wire, the tube being expandable by being supplied with fluid pressure, and the tube is configured to expand by being supplied with the fluid pressure and be able to press the operating rod or the operating wire against the fixed portion of the shaft part. a shaft part; a bendable part (2; 2A) whose proximal end is linked to a distal end of the shaft part, the bendable part (2; 2A) being bendable in a direction orthogonal to an axis of the shaft part; a forward end part whose proximal end is linked to the bendable part (2; 2A); an operating rod, or an operating wire, inserted through a groove or a hole of the shaft part and a groove or a hole of the bendable part (2; 2A), the groove or the hole of the shaft part being provided in a manner to extend along an axial direction of the shaft part, the groove or the hole of the bendable part (2; 2A) being provided in a manner to extend along an axial direction of the bendable part (2; 2A), the operating rod or the operating wire having a distal end thereof fixed to the bendable part (2; 2A); and a pressing portion configured to be able to press the operating rod or the operating wire against a fixed portion of the shaft part, wherein the bendable part (2; 2A) is configured to be bendable as a result of the operating rod or the operating wire being operated in an extending direction of the operating rod or the operating wire, and the operating rod or the operating wire is configured such that, when the operating rod or the operating wire is pressed against the fixed portion of the shaft part by the pressing portion, friction force is generated, and at a pressing position where the operating rod or the operating wire is pressed against the fixed portion of the shaft part, the operating rod or the operating wire is fixed in the axial direction by the friction force; characterized in that: the pressing portion includes a tube that is inserted through the groove or the hole of the shaft part adjacently to the operating rod or the operating wire, the tube being expandable by being supplied with fluid pressure, and the tube is configured to expand by being supplied with the fluid pressure and be able to press the operating rod or the operating wire against the fixed portion of the shaft part.