A light source device that radiates excitation light or emitted light by the excitation light, includes: an excitation light source that radiates the excitation light; a fluorescent wheel that includes a phosphor, which emits light in a predetermined wavelength range on reception of the excitation light, in a circumferential direction; a driving device that rotates the fluorescent wheel; and a shielding member that is arranged around the excitation light source and the fluorescent wheel and shields the excitation light and the emitted light, wherein an opening through which outside air is introduced is provided at a part of the shielding member.