PROBLEM TO BE SOLVED: To provide an optical adapter for endoscopes having a reduced diameter, hardly causing fracture of a mounting part thereof mounted on a distal end of an insertion part, and preventing fall.SOLUTION: An optical adapter 20 for endoscopes includes: a connection ring 22 configured to be attachable/detachable with respect to a distal end 8 of an insertion part 7 of an endoscope 1； an adapter-side screw part 27 that is provided on the connection ring 22, comes into contact with a distal-side first screw part 14a for fall prevention, provided at the distal end 8 so as to prevent the fall, and is threadedly engaged with a distal-side second screw part 14b for fixed installation, provided at the distal end 8； and an antislip-finished part 25 formed at an outer peripheral part of the connection ring 22 and provided at such a position not to be overlapped with the distal-side first screw part 14a in a state where the distal-side second screw part 14b and the adapter-side screw part 27 are threadedly engaged with each other.SELECTED DRAWING: Figure 5【課題】 細径化でき、且つ挿入部の先端との装着部分が破断し難く、脱落を防止する内視鏡用光学アダプタの提供。【解決手段】 内視鏡用光学アダプタ２０は、内視鏡装置１の挿入部７の先端部８に着脱自在な接続リング２２と、接続リング２２に設けられ、先端部８に設けられた脱落防止用の先端部側第１ネジ部１４ａに当接して脱落が防止されると共に、先端部８に設けられた装着固定用の先端部側第２ネジ部１４ｂに螺合するアダプタ側ネジ部２７と、接続リング２２の外周部に形成され、先端部側第２ネジ部１４ｂとアダプタ側ネジ部２７が螺合した状態において、先端部側１ネジ部１４と重畳しない位置に設けられた滑り止め加工部２５と、を具備する。【選択図】図５
