A backlight unit of a liquid crystal display device includes a prism light guide plate supported by a frame-like chassis. The light guide plate includes a light incident surface having two ends, near which stainless steel metal stoppers are attached respectively. The metal stoppers include pawls which, upon the attachment, come inward from sides of the light incident surface of the light guide plate to between the light incident surface and a lamp (lamp holders). When the liquid crystal display device is subjected to an impact from outside, the metal stoppers prevent the light guide plate from moving toward the lamp, thereby offering improved impact resistance.