PROBLEM TO BE SOLVED: To improve insertion property of an insertion part without lowering a light distribution performance.SOLUTION: An illumination optical system for an endoscope includes a cylindrical tip frame part 1 provided on an insertion part distal end of the endoscope and composed of a transparent member for transmitting illumination light from a light guide disposed at the insertion part, and a distal end surface 7 and a lens surface 3 provided in order from the distal end of the insertion part to a proximal end of the insertion part of the tip frame part. The distal end surface includes an inclined surface 8 which is inclined to at least part of the effective cross sectional area of the light guide from the insertion part distal end to the insertion part proximal end, and whose maximum inclination angle is at least 10° to a surface vertical to the center axis of the light guide. The lens surface includes a surface inclined for +10° or more and a surface inclined for -10° or less to the perpendicular of the center axis, in each of two divided cross sections for which a cross section including the center axis of the light guide is divided at the center axis.COPYRIGHT: (C)2013,JPO&INPIT【課題】配光性能を低下させることなく挿入部の挿入性を向上させる。【解決手段】内視鏡の挿入部先端に設けられ、該挿入部に配置されるライトガイドからの照明光を透過する透明部材からなる筒状の先枠部1と、該先枠部の前記挿入部先端から前記挿入部基端に向かって順に設けられた先端面7及びレンズ面3を備え、前記先端面が、前記挿入部先端から前記挿入部基端に向かい前記ライトガイドの有効断面積の少なくとも一部に対して傾斜し、その最大傾斜角が前記ライトガイドの中心軸に垂直な面に対して10°以上である傾斜面8を有し、前記レンズ面が、前記ライトガイドの中心軸を含む断面を前記中心軸で分割した二つの分割断面の各々において、前記中心軸の垂線に対して+10°以上傾斜する面と-10°以下傾斜する面とを含む内視鏡用照明光学系を提供する。【選択図】図2
