A light source apparatus includes an excitation-light source, a first light guiding member and a second light guiding member which guide excitation light emitted from the excitation-light source, a wavelength converting member which is installed near an emitting end of excitation light from the excitation-light source of the first light guiding member and the second light guiding member, and which receives excitation light which has been guided by one of the first light guiding member and the second light guiding member, and emits a wavelength-converted light of a wavelength different from a wavelength of the excitation light, a first light receiving element which is installed near the wavelength converting member, and which directly or indirectly receives the wavelength-converted light of which, the wavelength is converted by the wavelength converting member, and an optical path switching section which guides the excitation light to one of the first light guiding member and the second light guiding member according to an output of the first light receiving element.