A light source device has a blue solid-state light source, a red solid-state light source, a first retardation plate, a dichroic mirror, a phosphor plate, a second retardation plate, and a reflector. The first retardation plate causes light from the blue solid-state light source to have a phase difference. The dichroic mirror provides the light from the blue solid-state light source with polarization separation, receiving the light from the blue solid-state light source and light from the red solid-state light source in an identical direction. The phosphor plate emits fluorescence light, excited by one light, separated by the dichroic mirror. The second retardation plate converts, into circular polarization, polarization of the light from the red solid-state light source and other light, separated by the dichroic mirror. The reflector reflects light converted into circular polarization by being passed through the second retardation plate.