A surface light source device includes substrate, a plurality of light emitting devices disposed at constant intervals on substrate, and light diffusion plate disposed substantially parallel to substrate over the plurality of light emitting devices. Light emitting device includes light emitting element and light flux controlling member. A luminous intensity of light from light emitting device is gradually increased as an angle relative to optical axis becomes larger in an angular range from a direction along optical axis of light emitting device to a direction of emission of light with the highest luminous intensity from light emitting device. An angle of the light with the highest luminous intensity from the light emitting device is more than 78.7° relative to the optical axis. Surface light source device satisfies two Equations of H/P≦0.2, and I1/2/I0>6.