A plurality of convex strip portions are formed on a front surface (or a back surface) of a light guiding plate, extending in a direction from a light incidence plane to an opposite side surface. A concave portion is formed on a side surface of each convex strip portion. An inner wall of the concave portion is formed from at least two flat planes inclined with respect to three axial directions orthogonal to each other (X, Y and Z axial directions), respectively. Thereby, damage to the surface illuminant equipment such as a light guiding plate due to the interference between a back surface and units disposed on the back surface of the light guiding plate is prevented, while preventing a linear part with relatively low luminance from being viewed from the front surface of the light guiding plate.