A light source device of the present disclosure includes a light emitting device that outputs a first light having a first wavelength in a first polarization direction, a first optical element having a first area and a second area, a second optical element into which the first light reflected by the first area is entered, converting the first light into a circularly-polarized second light having the first wavelength, and a diffuser element into which the second light is entered. The second light entering the second optical element is converted into a third light having the first wavelength in a second polarization direction, the third light is transmitted through the first area, the second light is transmitted through the second area, and a fourth light output from the diffuser element and entered into the first area and the second area is transmitted through the first area and the second area.