An optical modulator capable of efficiently transmitting electric signals to an acting portion of a signal electrode with acting on an optical waveguide even when the electric signals are in high frequency zone, and capable of performing high frequency broad band operation. The optical modulator comprises a substrate (1) formed of a material having electro−optical effect, an optical waveguide formed on the substrate, and an electrode (3) for modulating the light passing through the optical waveguide. The optical modulator is characterized in that an electric signal connection pad unit (6) is proide on a part of the electrode, and in that the thickness of the substrate which is located at least on a lower part of the electric signal connection pad unit (6) and directly or indirectly continuous to the electric signal connection pad unit (6) made is smaller than the thickness of other parts of the substrate.
