A core layer has a light entrance region and a light exit region, said light entrance region having a width greater than said light exit region. The light entrance region has at least a side surface shaped as a reflecting surface. The light entrance region has an end having a parabolic shape. An LED is disposed in contact with a lower surface of the light entrance region. Signal light is introduced from the LED into the light entrance region with increased light entrance efficiency, and is highly efficiently reflected by the side surface of the light entrance region for higher light collecting efficiency.