A surface light source device is provided to prevent the generation of a bright line at a light-receiving region of a light guide plate and secure light uniformity over the entire region of the light guide plate. A surface light source device includes a light guide plate(10) and a light source(20). At least one optical element(30) is located between the light source and the light guide plate. The optical element has an optical structure plane that induces light generated from the light source to be diffused to the light guide plate. The optical element includes a first optical element(31) located at the side of a light-projecting face of the light source and a second optical element(33) that is located at the side of a light-receiving face of the light guide plate and has an optical structure plane(33a) forming a light diffusion angle greater than the light diffusion angle formed by an optical structure plane(31a) of the first optical element.
