A backlight device is incorporated into a liquid crystal display device so as to illuminate a liquid crystal panel from a backside. The backlight device includes a light-guiding plate emitting a light, which is incident on a side surface thereof, from a front surface, and a reflector arranged along the side surface of the light-guiding plate so as to reflect a light from a light source accommodated inside thereof and guide the light to the side surface of the light-guiding plate through an opening part. A least one minute protruding part, which protrudes in a direction parallel to the side surface of said light-guiding plate, is formed on an edge part of the opening part of the reflector facing the light-guiding plate. The side surface of the light-guiding plate is brought into contact with the protruding part of the reflector when the light-guiding plate moves toward the reflector.