A light guide plate includes a light exit plane and a light entrance end, is formed into a shape having a thickness in a direction orthogonal to the light exit plane, the thickness being gradually larger as being farther from the light entrance end, and contains scattering particles dispersed therein, and a light guide plate assembly includes the light guide plate and a prism sheet which includes a plurality of prisms arrayed in parallel with each other, and is arranged so that vertex angles of the prisms face the light exit plane. The scattering particles scatter light entering from the light entrance end and propagating in the light guide plate, which satisfy Expressions (1) and (2) below, and vertex angles of the prisms of the prism satisfy Expression (3) and (4) below. 1.1≦ΦNPLGKC≦8.2  (1) 0.005≦KC≦0.1  (2) 55°≦θ≦80°  (3) 0°≦θ1≦15° and 30°≦θ2≦45°  (4)