[PROBLEM] Providing an optical source that outputs optical frequency modulated light having a constant output optical intensity.[MEANS FOR SOLVING THE PROBLEM] Provided is a light source apparatus that outputs an optical signal having an optical frequency corresponding to a frequency control signal, the light source apparatus including a laser light source section that outputs laser light having an optical frequency corresponding to the frequency control signal; and an optical intensity adjusting section that compensates for intensity change of the laser light to output laser light in which the intensity change caused by a change in the optical frequency is restricted. The optical intensity adjusting section includes an optical amplification section that adjusts an amplification factor of the laser light from the laser light source section, based on the frequency control signal, to restrict the intensity change of laser light corresponding to the frequency control signal, and outputs the resulting laser light.