A light source device according to the present disclosure includes a light source unit configured to emit a first light beam, a second light beam, and a third light beam, a first polarization split element configured to transmit the first light beam and the second light beam and reflect the third light beam, a second polarization split element configured to transmit the first light beam and reflect the second light beam, a first retardation element, a first diffusion element configured to diffuse the third light beam, a second diffusion element configured to diffuse the second light beam, and a third diffusion element configured to diffuse the first light beam. The first retardation element converts a polarization direction of the second light beam from the first polarization split element, and converts a polarization direction of the another part of the second light beam from the second polarization split element.