To provide a multi-wavelength light source which is mechanically stable and is capable of generating constant multi-wavelength lights with a wide optical frequency interval.

This source is provided with two pieces or three pieces of light sources 11 outputting lights whose frequencies are different each other, an optical frequency stabilizing means stabilizing optical frequencies of respective light sources 11 and controlling an optical frequency interval to Δf and a nonlinear optical medium 13 generating the mixed light of plural four optical waves whose optical frequency interval is Δf by an optical parametric effect by inputting lights outputted from the respective light sources 11. The optical frequency stabilizing means controls the optical frequency interval of respective light sources 11 to Δf by using an array waveguide diffraction grating type optical filter 14.