A light incident into a wedge type light scattering conducting element from a light incident surface of the light scattering conducting element is converted into a light flux having a directionality and is output from a light output surface. The output light is input to a wedge type emitting direction characteristic adjusting element arranged with a positional relationship complementary to the light scattering conducting element. A prism shaped irregularity for adjusting a propagating directionality of the light in longitudinal/transverse directions is formed on a light input surface/light output surface of the wedge type emitting direction characteristic adjusting element. The wedge type emitting direction characteristic adjusting element has a weakened scattering power depending on requirements, thereby a degree of directionality sharpness of the light emitted from a surface light source device is adjusted. Various modifications are provided for the light scattering conducting elements, and regions having different scattering powers are combined for various patterns. The device is useful for A backlight source.