To reliably keep an LED board and a heat conductive member in close contact to improve the heat-dissipation efficiency and to reliably position an LED and an optical element, such as a lens part, arranged in a housing are a slim LED board, the housing that has an accommodating concave part to house the LED board, a heat conductive member that is arranged between the LED board and the accommodating concave part, a pressing member that has the lens part and that presses a long side edge part of the LED board against a bottom surface of the accommodating concave part of the housing, a securing mechanism for securing the LED board, the heat conductive member and the pressing member to the housing, and a positioning mechanism for positioning the lens part relative to the LED.