An illumination apparatus includes: a light-guiding portion including a light-introducing opening through which light is introduced from a light-emitting portion of an image pickup apparatus, a reflective surface that reflects light introduced from the light-introducing opening toward an image pickup optical axis of the image pickup apparatus, and a diffusion portion that diffuses the light reflected by the reflective surface toward an object as diffused light; and a reflective body including an opening portion allowing an image pickup opening of the image pickup apparatus to be exposed, and a reflective portion provided around the opening portion and including a reflective surface formed to expand from the opening portion toward the object, wherein the diffusion portion is disposed at a part of the reflective portion and the reflective body includes a wall portion extending to the object side at a boundary between the opening portion and the diffusion portion.