From the side putting on the rear over lap above direction 180 degree of endoscope, at least vis-a-vis the longitudinal direction of the endoscope, it uses the specified range combining with observation possible objective optical system, objective optical system the observation possible specified range the illumination optical system for the endoscope which possesses lighting possible illumination optical system. As for illumination optical system, light distribution property of the longitudinal direction of the endoscope, has the light distribution property which becomes the medium coming out, light of the medium coming out tries to irradiate the lateral vicinity vis-a-vis the longitudinal direction of the endoscope.内視鏡の周方向180度以上にわたり、少なくとも内視鏡の長手方向に対して側方から後方にかけての所定範囲を観察可能な対物光学系と組み合わせて用いる、対物光学系が観察可能な所定範囲を照射可能な照明光学系を有する内視鏡用照明光学系。照明光学系は、内視鏡の長手方向の配光特性が、中抜けとなる配光特性を有し、中抜けの光が内視鏡の長手方向に対して側方近傍を照射するようにする。
