A light source device includes an excitation light source that generates excitation light, a phosphor wheel including a phosphor segment that generates fluorescent light by excitation of the excitation light, and a mirror that guides the excitation light from the excitation light source to the phosphor wheel and emits the fluorescent light from the phosphor wheel as illumination light. The phosphor wheel further includes an anisotropic diffusion and reflection unit that diffuses and reflects incident excitation light such that an optical path for the incident excitation light and an optical path for the diffused excitation light after incidence of the excitation light are not overlapped. The mirror includes a first region that reflects the excitation light and transmits the fluorescent light and a second region that transmits the fluorescent light and the diffused excitation light which the anisotropic diffusion and reflection unit has diffused and reflected.