A light source apparatus includes a laser oscillator equipped with a first optical resonator, a plurality of second optical resonators including input portions respectively connected in parallel to the first optical resonator, a plurality of light extraction units configured to extract a light beam from an output portion of each second optical resonator, and a light multiplexing unit configured to multiplex the light beam extracted from each light extraction unit, wherein the light source apparatus causes the light multiplexing unit to output a multiplexed light beam passed through the plurality of second optical resonators, an optical member having refractive index dispersion and an optical amplification medium are disposed in each of the plurality of second optical resonators, and the optical amplification media of the plurality of second optical resonators are different from each other in maximum gain wavelength.