There is provided a surface light-emitting device capable of preventing an increase in power consumption even if the length of the light-emitting surface of the surface light-emitting device is greater than the width, and capable of emitting light uniformly without decreasing the brightness of the light-emitting surface nor increasing the height of the light guiding space. In the present surface light-emitting device, the incident plane (201) is one of two sides of the light guiding space (20) in opposition in the longitudinal direction. The light-transmitting plate (4) includes a diffusion filter (6) which covers a specific area of the surface of the light-transmitting plate (4) near the light source (3). The remaining area of the surface of the light-transmitting plate at a distance from the light source (3) is not covered with the diffusion filter (6). The diffusion filter (6) is formed of a laminate in which a plurality of diffuse transmission films are layered. The number of diffuse transmission film (6) layers is highest in the area closest to the light source (3) so that the light transmittance is increased as the distance from the light source (3) increases due to a decrease in the diffusion of light, and the number is gradually decreased as the distance from the light source (3) increases.