To provide a vibration detecting apparatus capable of outputting a digital vibration detection signal with a simple construction.

The apparatus includes a -modulator using variation of a diffraction angle of laser light L caused by displacement of a vibration membrane 11 and variation of a diffraction angle of the laser light L caused by wavelength modulation of the laser light L as feedback parameters for a laser light source 13. Any A-D converter (AD) complicated in structure and the like are not required, vibration of the vibration membrane 11 is digitally detected as a binarized audio signal Sout with a simple construction. In addition, since variation of a diffraction angle of the laser light L, instead of displacement of the vibration membrane 11 itself, is used as a feedback parameter, a whole of the apparatus also becomes a simple and easy construction.