An illumination optical system for an endoscope provided in an elastic insertion tube of an endoscope, comprising: two light guides disposed in the insertion tube to be arranged in a first direction to sandwich a center of the insertion tube therebetween an observation window disposed on a tip end face of a tip portion of the insertion tube two concave lens parts having negative powers, the two concave lens parts being disposed to sandwich the observation window at positions facing end faces of the two light guides on the tip end face of the insertion tube, and wherein: on the tip end face of the tip portion of the insertion tube, the end face of each of the two light guides has a smaller width in the first direction than a width thereof in a second direction perpendicular to the first direction each of the two concave lens parts has a larger negative power in the first direction than a negative power thereof in the second direction and of illumination light which has propagated through each of the two concave lens parts after being emitted from each of the two light guides, an optical path of light which has propagated through a center of each of the two light guides and has been emitted from a center of each end face of each of the two light guides is inclined outward in the first direction with respect to an axis direction of the insertion tube.La présente invention concerne un système optique déclairage pour un endoscope disposé dans un tube dinsertion élastique dun endoscope, comprenant : deux guides optiques disposés dans le tube dinsertion de manière à être agencés dans une première direction pour coincer le centre du tube dinsertion entre eux une fenêtre dobservation disposée sur une face dextrémité de pointe dune partie de pointe du tube dinsertion deux parties de lentilles concaves ayant des puissances négatives, les deux parties de lentilles concaves étant disposées de manière à coincer la fenêtre dobservation à des positions faisant face aux faces dextré
