PROBLEM TO BE SOLVED: To solve the difficulty in that the outer diameter of an endoscope illumination system in the optical axis orthogonal direction is suppressed to a smaller value, this difficulty being derived from that the light distribution lens is difficult to design to a smaller diameter.SOLUTION: An endoscope illumination optical system comprises: an optical fiber and a light guide rod member which is disposed at a pre-stage of the optical fiber emission end and transmits and emits incident light from the emission end. The light guide rod member includes: a rod main body disposed at the pre-stage of the emission end and a rod distal end disposed at a pre-stage of the rod main body. The rod main body has no segment in which the cross-sectional area in the optical axis orthogonal direction increases from the proximal end on the emission end side toward the distal end, and is shaped to monotonously taper down in at least one segment. The rod distal end has a shape extended higher than the distal end of the rod main body over the whole circumference with respect to the optical axis orthogonal direction.SELECTED DRAWING: Figure 2COPYRIGHT: (C)2018,JPO&INPIT【課題】配光レンズを小径に設計することが難しいことから、内視鏡用照明光学系の光軸直交方向の外形寸法を小さく抑えることが難しい。【解決手段】内視鏡用照明光学系は、光ファイバと、光ファイバの射出端の前段に配置され、該射出端より入射される光を伝送して射出する導光ロッド部材とを備える。導光ロッド部材は、射出端の前段に位置するロッド本体部と、ロッド本体部の前段に位置するロッド先端部とを有する。ロッド本体部は、射出端側に位置する基端から先端に向かって光軸直交方向の断面積が増加する区間が無く且つ少なくとも一部の区間で単調減少する形状を有している。ロッド先端部は、光軸直交方向に対して全周に亘り、ロッド本体部の先端よりも突出した形状を有している。【選択図】図2
