A light guiding plate is made of a transparent thermoplastic resin and has a first main surface, a second main surface opposed to said first main surface, a first side wall, a second side wall, a third side wall opposed to said first side wall and a fourth side wall opposed to said second side wall. The surface portion of the first main surface is provided with convex portions and/or concave portions, and the light guiding plate has a longitudinal-direction length, which is a length from the first side wall to the third side wall, of 40 mm or more but 130 mm or less, at least 80% region of the light guiding plate has a thickness of 0.1 mm or more but 0.55 mm or less.