A backlight unit for a liquid crystal display device includes a light source element, a light guide plate for guiding the output light from the light source element, and a frame for housing the light guide plate. The light source element is mounted on a flexible wiring substrate fixed to the liquid crystal display panel at one end thereof, together with an electronic component. The light source element and the electronic component are attached to the frame in such a way that each of the light source element and the electronic component is placed in a housing concave portion formed on the back surface side of the frame, by bending the flexible wiring substrate. A case is fixedly attached to the flexible wiring substrate to cover the electronic component. Then, the case is fixed to the inside of the housing concave portion.