An irradiation device (101, 201) comprising: - a light source that is adapted to emit light; - a transparent bar-shape light guide (110, 210) having the light source disposed near an end of the light guide (110, 210); - a first diffusion/reflection portion (121, 184) which is provided so as to extend in a lengthwise direction of the light guide (110, 210), and which is adapted to diffuse and reflect light propagating through the interior of the light guide (110, 210); - a first light outgoing area which is a portion of an outer surface of the light guide (110, 210) extending in the lengthwise direction and located in a reflection direction of the first diffusion/reflection portion (121, 184), and which is adapted to emit, as primary light, light reflected by the first diffusion/reflection portion (121, 184); - a second diffusion/reflection portion (123, 185) which is provided so as to extend in the lengthwise direction of the light guide (110, 210), and which is adapted to diffuse and reflect light propagating through the interior of the light guide (110, 210); - a second light outgoing area which is a portion of the outer surface of the light guide (110, 210) extending in the lengthwise direction and located in a reflection direction of the second diffusion/reflection portion (123, 185), and which is adapted to emit, as secondary light, light reflected by the second diffusion/reflection portion (123, 185); and - a plane mirror that is adapted to reflect the secondary light in a direction overlapping the primary light in a predetermined area, wherein the second light outgoing area has a curvature as viewed in the lengthwise direction of the light guide (110, 210); characterized in that: - the first light outgoing area at least partially includes a plane or a curved face having a smaller curvature than the second light outgoing area as viewed in the lengthwise direction; and - the primary light has a wider divergence angle than that of secondary light. - a light source that is adapted to emit light; - a transparent bar-shape light guide (110, 210) having the light source disposed near an end of the light guide (110, 210); - a first diffusion/reflection portion (121, 184) which is provided so as to extend in a lengthwise direction of the light guide (110, 210), and which is adapted to diffuse and reflect light propagating through the interior of the light guide (110, 210); - a first light outgoing area which is a portion of an outer surface of the light guide (110, 210) extending in the lengthwise direction and located in a reflection direction of the first diffusion/reflection portion (121, 184), and which is adapted to emit, as primary light, light reflected by the first diffusion/reflection portion (121, 184); - a second diffusion/reflection portion (123, 185) which is provided so as to extend in the lengthwise direction of the light guide (110, 210), and which is adapted to diffuse and reflect light propagating through the interior of the light guide (110, 210); - a second light outgoing area which is a portion of the outer surface of the light guide (110, 210) extending in the lengthwise direction and located in a reflection direction of the second diffusion/reflection portion (123, 185), and which is adapted to emit, as secondary light, light reflected by the second diffusion/reflection portion (123, 185); and - a plane mirror that is adapted to reflect the secondary light in a direction overlapping the primary light in a predetermined area, - the first light outgoing area at least partially includes a plane or a curved face having a smaller curvature than the second light outgoing area as viewed in the lengthwise direction; and - the primary light has a wider divergence angle than that of secondary light.