Provided is a light source device where the number of optical components is reduced without lowering an efficiency for light utilization. The light source device includes an excitation light source which generates blue laser light as excitation light, a phosphor wheel including a phosphor which is excited by the excitation light from the excitation light source to generate yellow fluorescent light, and a mirror which guides the excitation light from the excitation light source to the phosphor wheel and transmits the fluorescent light from the phosphor wheel, wherein the mirror includes a first region which reflects the excitation light and transmits the fluorescent light and a second region which transmits the fluorescent light and diffused excitation light which is diffused and reflected in the phosphor. The yellow fluorescent light and the diffused excitation light passing through the mirror are mixed to generate white light.