A treatment instrument insertion conduit 50 which is provided in the insertion portion and in which an insertion passage 51 through which the treatment instrument is inserted is formed in the tubular partition wall 52 and a part of the partition wall 52 of the treatment instrument insertion conduit 50 Which is more flexible than the other partitions 52 having a predetermined length in the circumferential direction C of the partition wall 52 and is pressed from the outside of the partition wall 52 so that it is radial in the treatment instrument insertion duct 50 And a deformable portion 58 which is deformable toward the insertion passage 51 side in K and which is capable of partially reducing the diameter of the insertion passage 51.挿入部と、挿入部内に設けられるとともに、管状の隔壁52内に処置具が挿通される挿通路51が構成された処置具挿通管路50と、処置具挿通管路50の隔壁52の一部において隔壁52の周方向Cに所定の長さを有して構成された、他の隔壁52の部位よりも柔軟であるとともに隔壁52外から押圧されることにより処置具挿通管路50の径方向Kにおいて挿通路51側へと変形自在であり、挿通路51の径を部分的に縮径自在な変形部58と、を具備している。
