A light guide plate includes a light incidence surface, a light reflection surface, and a light emission surface. The light emission surface forms a plurality of light-guiding structures, which are extended in a direction substantially perpendicular to a lengthwise direction of a light source. The light-guiding structures have a substantially V-shaped cross-section and, among the light-guiding structures, those arranged in opposite endwise zones of the light emission surface in the lengthwise direction have an irregular V-shaped cross-section defined by a long inclined side, which faces endwise, and a short inclined side. The long and short sides respectively form first and second inclined angles with respect to the light emission surface and the first included angle is smaller than the second included angle and the first inclined angle gets smaller with the associated light-guiding structure located closer to the lengthwise end.