A light source apparatus includes an optical resonator provided with a plurality of gain media that amplify light and an optical waveguide and a control unit configured to individually control amplification factors of the plurality of gain media, in which the plurality of gain media have mutually different maximum gain wavelengths whose amplification regions are mutually partially overlapped, and a wavelength at which a total gain by the plurality of gain media becomes a maximum value is set to be variable on the basis of the control on the amplification factors.
