A first light source device includes: a solid-state light source; a condenser element that collects light from the solid-state light source; a retardation plate that converts linearly polarized light into circularly polarized light; and a reflection plate, wherein the retardation plate is disposed at a point of incidence of collected light and divergent light between the condenser element and the reflection plate. A second light source device includes: a solid-state light source; a retardation plate that changes a polarization direction of light from the solid-state light source to make a ratio of polarization and s-polarization components of the light constant under control; and a dichroic mirror that separates the light from the retardation according to the polarization direction, wherein the retardation plate is disposed at a point of incidence of one of collected light and divergent light between the solid-state light source and the dichroic mirror.