A light source device according to the present disclosure includes: a plurality of solid-state light source units; a polarization combination mirror for combining polarized lights incident from the plurality of the solid-state light source units; a half-wavelength plate having a strip shape, for converting a polarization azimuth of one of polarized lights coming from the polarization combination mirror; another half-wavelength plate for controlling proportions of intensities of polarization components of the polarized lights incident from the former half-wavelength plate; a dichroic mirror for separating the polarized lights incident from the latter half-wavelength plate; a phosphor plate for emitting light, upon being excited by the polarized light having been separated by the dichroic mirror.