It is an object to provide a planar lighting device that is a thin and light in weight, that emits light without luminous unevenness and that is capable of achieving increased dimensions.Provided is a planar lighting device comprising: a light source that emits light; and a light guide plate disposed opposite the light source in which light emitted from the light source enters and is emitted therefrom as planar light, wherein: the light guide plate comprises a flat light exit plane that emits the planar light, a light entrance plane that is formed opposite the light source and includes one side of the light exit plane, an end plane that includes the opposite side to the one side of the light exit plane, and a rear plane formed on the side opposite the light exit plane; the rear plane comprises a first rear plane that is joined with the end plane and is inclined so that the distance from the light exit plane increases as the distance from the end plane increases, and a second rear plane that is joined with the first rear plane and is joined with the light entrance plane; and the first rear plane and the second rear plane are joined so as to form a joining line where the distance from the joining line to the light entrance plane is shorter than the distance from the joining line to the end plane, and the distance between the light exit plane and the rear plane is greatest at the joining line.