To reduce uneven color regarding a surface light source device and an image display device.

The surface light source device includes a light guide plate 6 guiding light emitted from a light-emitting diode 13 and having a light-emitting surface 6a and a light-emitting acceleration surface 6c, and an intermediate light guide section 10 located to face to an outer periphery 6e of the light guide plate and a sealing section 15 of a light-emitting diode package 12. The light-emitting diode package is arranged by separating it in the thickness direction of the light guide plate, and a total refractive surface 10c is formed on the intermediate light guide section. When a refractive index of the light guide plate is denoted by n and the thickness of the light guide plate is denoted by L1 and a distance between the light-emitting diode arranged at a side nearest to the light emitting acceleration surface and a position where the light internally reflected by the total refractive surface reaches the light emitting acceleration surface of the light guide plate is denoted by L3 and a width of the light-emitting diode in the thickness direction of the light guide plate is denoted by L4, the distance L3 satisfies following relations of L3L1tan{sin-1(1/n)}+(L1-L2-L4)tan{sin-1(1/n)} and L3L2tan{sin-1(1/n)}.