A light source device according to the present disclosure includes a light source section, a first polarization split element for transmitting first light with a first polarization direction from the light source section and reflecting the first light with a second polarization direction, a first retardation element, a second polarization split element for reflecting the first light in the second polarization direction from the first retardation element, a second retardation element, and a light conversion device having a diffusion element for diffusing the first light from the second retardation element, a first wavelength conversion element for performing wavelength conversion on the first light to emit second light, and a substrate.