A light source device includes a light emitting element emitting light of a first wavelength band, a fluorescent wheel and a mirror. The fluorescent wheel includes a fluorescent area converting the light of the first wavelength band into fluorescent light and a reflection area reflecting the light of the first wavelength band. The minor reflects a component in a first polarization direction of the light of the first wavelength band and transmits a component in a second polarization direction orthogonal to the first polarization direction. The reflection area includes a reflecting surface and a polarization conversion layer including an optical axis and converts either the first or second polarization direction to another polarization direction. The optical axis of the polarization conversion layer is inclined by 45 degrees to a polarization direction of the light of the first wavelength band at an irradiation position thereof in the fluorescent wheel.