The endoscope illuminating optical system includes a transparent resin member, and a lighting member which outputs illumination light. The transparent resin member has a through hole in which an image sensor is disposed, a non-through hole in which the lighting member is disposed, an internal optical surface which is formed at an interior of the transparent resin member by the non-through hole, and an outer surface from which the illumination light incident on the transparent resin member via the internal optical surface, is emerged toward an object. The outer surface has a curved-surface area through which the illumination light passes, and the curved-surface area has a boundary with the through hole. In the curved-surface area, a displacement of each point of the curved-surface area from the boundary occurs in a direction away from the object.