Provided are: a light source device which can reduce the amount of light that escapes from a light-entering surface of a light guide plate in an edge light-type light source device, and which can maintain high display quality; and a display device employing the light source device. The light source device comprises a light guide plate having a rectangular shape, and a substrate having a strip shape on which light emitting diodes are mounted on a surface that faces a side surface of the light guide plate. A plurality of peripheral walls are provided on the substrate so as to enclose at least one of the light emitting diodes. Each of the plurality of peripheral walls has a light reflective inner surface and has a height equal to or greater than the facing distance between the light guide plate and the substrate.