The light source device includes a rear vessel, a light source substrate, a plurality of light-emitting diodes, a front cover, and a light diffuser. The rear vessel has a bottom plate and a first lower side plate connected to the bottom plate. The light source substrate is accommodated in the rear vessel. The plurality of light-emitting diodes is located over the light source substrate. The front cover has an upper plate and a first upper side plate connected to the upper plate, is located over the rear vessel, and accommodates the rear vessel. The light diffuser is accommodated in the front cover, is located over the plurality of light-emitting diodes, and is spaced away from the plurality of light-emitting diodes. The first lower side plate and the first upper side plate each have a notch.