An illumination apparatus includes an outer tube, an inner tube, and a light source. The outer tube has a reflecting inner wall. The inner tube is disposed in the outer tube and coaxial with the outer tube. The inner tube has a reflecting outer wall. A ring-shaped light channel is formed between the outer tube and the inner tube. The ring-shaped light channel has a light entrance and a light exit corresponding to two ends of the outer tube respectively. A segment of the inner tube protrudes from the light exit. The light source is disposed at the light entrance. A light beam emitted from the light source enters the ring-shaped light channel through the light entrance, is reflected multiple times by the reflecting inner wall of the outer tube and the reflecting outer wall of the inner tube, and travels out of the illumination apparatus through the light exit.
