A light source device includes: a light emitting plate that has a plurality of segment regions including a transmissive portion that transmits light and a reflective portion on which a fluorescent substance layer; a light source that irradiates the fluorescent substance layer of the light emitting plate with the excitation light; a dichroic mirror that is disposed between the light source and the light emitting plate to transmit the excitation light and reflect fluorescent light from fluorescent substances of the fluorescent substance layer; and an optical device that condenses the excitation light transmitted by the transmissive portion of the light emitting plate and the fluorescent light reflected by the dichroic mirror on a single optical path to form a condensed light and radiate the condensed light toward the same direction.