Alight source device according to the present disclosure includes a light source section configured to emit first light in a first wavelength band, a first optical element configured to collect the first light emitted from the light source section, a second optical element having a first plane of incidence and a first exit surface, and a wavelength conversion element having a second plane of incidence and a second exit surface, and configured to convert the first light entering the wavelength conversion element through the second plane of incidence into second light having a second wavelength band, wherein the second optical element and the wavelength conversion element are disposed in a state in which the first exit surface and the second plane of incidence are opposed to each other at a distance from each other, and the second plane of incidence is larger in size than the first exit surface.