To expand the diameter reduction and the inner space of the insertion portion or the like, and to provide an endoscope having a fixing mechanism and the fixing mechanism thereby improving the assembling workability. Fixing mechanism includes a tubular member 40, the ring member 80 to the tubular member 40 therein is fixed, and the recesses 41A, 41B provided on the outer peripheral surface of the cylindrical member 40, recessed portions 41A, around the axis in 41B a first 43 formed in the direction, the second 42a formed in the axial direction, and 42b, provided on an inner peripheral surface of the ring member 80, the convex portion engaged in the recess 41A, 41B 81A, and 81B, a first contact portion 83 which abuts the first 43 in the axial direction, and a second contact portion 82a, 82b abutting on the second in the direction about the axis, comprising a.挿入部等の細径化及び内部空間の拡大を図り、且つ、組付け作業性の向上を図った固定機構及び固定機構を有する内視鏡を提供する。固定機構は、筒状部材40と、内部に筒状部材40が固定されるリング部材80と、筒状部材40の外周面に設けられた凹部41A、41Bと、凹部41A、41Bにおいて軸周りの方向に形成される第1の凹壁43と、軸方向に形成される第2の凹壁42a、42bと、リング部材80の内周面に設けられ、凹部41A、41Bに係合する凸部81A、81Bと、軸方向において第1の凹壁43に当接する第1の当接部83と、軸周りの方向において第2の凹壁に当接する第2の当接部82a、82bと、を具備する。
