A light source apparatus includes a light source optically connectable to a scope including a light guide configured to guide light, and first and second illumination light emission units configured to radiate illumination light based on the guided light on a subject, and a light quantity distribution changing device disposed on an optical path of the light emitted from the light source. The light quantity distribution changing device is configured to control a light quantity of the light brought into each of the first illumination light emission unit and the second illumination light emission unit, so as to change a light quantity distribution of the illumination light radiated on the subject.