To provide an optical heterodyne interferometer to provide resolution same as the case where a laser beam having a short wavelength is used, using a laser beam having a long wavelength without actually using the laser beam having the short oscillating wavelength as a light source.

In this heterodyne device, the first polarized light group comprising plural spectral lines and having the same polarized direction, and the second polarized light group comprising a single spectral line or plural spectral lines and having polarization orthogonal to the first polarized light group are superposed, a pair having a sum of at least one wave number is formed out of light beats generated by superposing orthogonal lights of a heterodyne interferometer where the first polarized light group passes one side of interference arms and where the second polarized light group passes the other side of the arm, and the pair is multiplied by itself (double heterodyne is conducted) to make a beat having a superposed wavelength with a wave number comprising the sum of the wave numbers.