A primary object of the present invention is to provide a surface light source device attaining a homogenous luminance distribution on a light emitting surface of a light guiding plate in which a dot light source having a high directivity of emitted light is employed. The device includes: a light guiding plate 5 including a plurality of primary holes in such a manner as to locate each dot light source 3 inside; and dot printing 7a being employed as an auxiliary light source means which diffuses light from the dot light source 3 to the position between dot light sources 3 being adjacent to each other, wherein the dot printing 7 is provided at a base of the light guiding plate 5 and a middle point of the connected dot light sources 3 being adjacent to each other.