An illumination unit includes a distal end frame member having a through opening, a plurality of illumination sections, and a holding member which is arranged in the through opening and holds the illumination sections to incline the illumination sections at a desired angle with respect an opening surface of the through opening and to form a cascade along the axial direction of the through opening. The illumination unit includes a reflective member which is configured to reflect the illumination light emitted from the illumination sections toward the opening surface, the reflective member being held by the holding member to face the illumination sections and to apply the illumination light externally emitted from the illumination sections from the inside of the through opening via the opening surface.
