A light source system includes an excitation light source, a fluorescent plate that emits fluorescence when exposed to the excitation light from the excitation light source, and a compartment storing the fluorescent plate. The compartment has a heat-receiving section and a heat-dissipation section thermally connected to each other. The heat-receiving section is located opposite a fluorescence light output side of the fluorescent plate, in the compartment. The heat-dissipation section is outside the compartment.