An illumination device comprises a light source like a halogen lamp, a light guide, a round rod-shaped transparent radiation member having a proximal end and a distal end, and a transparent radiation plate. The light guide is a plastic optical fiber comprising a single core of silicon rubber and a cladding layer of tetrafluoroethylene/hexafluoropropylene copolymer. The radiation member is a transparent circular cylinder made of acrylic resin, and has a predetermined pattern of light scattering regions on its surface oppose the directions where the light is radiated. The radiation plate is placed such a position that one side plane of the radiation plate oppose to he radiation member, and also has a predetermined pattern of light scattering regions on the back. The light scattering regions are provided along said radiation member in such a way that a ratio of an tea of one region to that of adjacent region becomes larger as the one region becomes distant from the proximal and of the radiation member.