An acousto-optic device is disclosed which can achieve both of suppression of secular change and prevention of device damage and can maintain a stabilized wavelength selection filtering operation. The acousto-optic device includes a substrate on which a SAW guide for guiding a surface acoustic wave and an optical waveguide for guiding an optical wave are provided. A pyro-electricity coping conductive wiring pattern is provided in a region of the substrate other than the SAW guide and neutralizes polarization charge generated on a surface of the substrate.