An illumination device comprising a light guide bar, a light source and a reflective sleeve is provided. The light guide bar comprises a first end surface, a second end surface, and a cylindrical surface. The cylindrical surface is disposed between the first end surface and the second end surface and has a light-emitting surface and a reflective surface. The light source is disposed at the outside of the first end surface of the light guide bar. The reflective sleeve covers the second end surface of the light guide bar and has a reflective cavity, which tapers inward to form a vertex angle. A part of the incident light of the light source is reflected to the light-emitting surface via the reflective surface by the reflective cavity or directly reflected to the light-emitting surface by the reflective cavity.