In the related art, a known illumination device provided at the distal end of an endoscope uses a C-ring-shaped light-guiding member disposed around an imaging optical system (for example, see Patent Literature 1). To observe an observation target site in detail with an endoscope, there are cases where the distal end surface of the endoscope is brought into contact with the observation target site. At that time, when the distal end surface of the endoscope is disposed at an angle with respect to the surface of the observation target, the distance between the lower portion of the distal end surface of the endoscope and the observation target site decreases, and the illumination light becomes partially brighter, thus causing halation in the lower region in the endoscope image. In Patent Literature 1, halation is prevented by using a C-ring-shaped light-guiding member, a part of which is removed at the lower side of the distal end surface of the endoscope.
Furthermore, in the illumination device in Patent Literature 1, a reflection surface having an indentation/projection structure is provided on a back surface located on the opposite side from the emission surface of the light-guiding member, and the illumination light guided in the light-guiding member is reflected in various directions by this reflection surface, whereby the illumination light is efficiently emitted from the emission surface.