Illumination light emitted from a light source is efficiently distributed to an observation target, and luminous intensity distribution performance is enhanced. An endoscopic illumination optical system, including a light guide bundle 10 for guiding illumination light emitted from a light source, the light guide bundle being provided in an insertion portion of an endoscope device, and an illumination lens 11 for distributing the illumination light emitted from the light guide bundle to an observation target, wherein the illumination lens includes two points of inflection P in a vertical cross section including an optical axis of the lens, and includes a first concave surface 11a that is located on an inner side of the two points of inflection, and an annular second concave surface 11b that is located on an outer side of the two points of inflection and that is continuous with an outer periphery of the first concave surface, the second concave surface being arranged so as to face an outer peripheral edge of the light guide bundle in an optical axis direction.
