Surface Light Source Device

A surface light source device, wherein:

• a plurality of point-like light sources of which respective exit directions of light are parallel with one other are disposed on a same plane such as to be spaced apart two-dimensionally and are disposed such that, on four edges and within an area surrounded by the four edges of a quadrangle of which the apexes are light emission centers of four predetermined light sources, a light emission center point of a light source other than the four light sources is not included;
• a light diffusing member having a first surface that opposes the light sources and a second surface on the side opposite of the first face, in which light emitted from each light source enters the first surface and exits the second surface in a dispersed state, is disposed in a position on the exit direction side in relation to the plurality of light sources such as to be parallel with the plane;
• projections having a predetermined pyramid shape are formed in an array on the second surface of the light diffusing member;
• and
• a virtual bottom surface of the projection positioned on the second surface is configured by a plurality of linear bottom edges, and all bottom edges are disposed as skew lines in relation to the four edges and the diagonal lines of the quadrangle.