A liquid crystal display device comprising a liquid crystal display panel, a backlight and a heat sink member is disclosed. The backlight comprises a light-guiding plate disposed on one principal surface side of the liquid crystal display panel, LED light sources disposed on an end surface of the light-guiding plate, a mounting board for mounting the LED light sources thereon and a thermally conductive member connected to the mounting board. The heat sink member is connected to the mounting board through the thermally conductive member.