Abstract: An apparatus optically reproduces FM electric signals from the recording medium recorded with said electric signals in the form of a change in refraction index. The apparatus is so constructed that a pair of laser beams are incident on the recording medium at substantially the same point with an angle defined between the laser beams; a diffracted light obtained by causing each of said beams to be diffracted, upon being transmitted through the recording medium, in accordance with the phase change pattern thereof is overlapped on a non-diffracted light obtained by causing the each of said beams to be transmitted through the recording medium without being diffracted; and optically phase-modulated signals are detected as a beat output produced by optical mixing of the diffracted light with the non-diffracted light, thus to reproduce a recorded signal.