In an acoustoelectric converter element, a light wave from a light source is introduced into a first optical waveguide of a vibration substrate, and diffracted by a diffraction grating disposed on the first optical waveguide. The diffracted light is directed to and detected by a photo detector. Here, the vibration substrate is so supported as to vibrate with respect to an acoustic wave. Therefore, the diffracted light detected by the photo detector is modulated by the acoustic wave, and a signal is output from the detector in accordance with the acoustic wave.