In an optical modulator of the invention, a signal electrode and a ground electrode are formed along a pair of branching waveguides of a Mach-Zehnder type optical waveguide, and a first region positioned on an input side of an interaction section of light and an electric signal is made a forward modulation section, and a second region positioned on an output side is made an inverse modulation section, and a spacing or the like of the signal electrode and the ground electrode is optimized so that that a loss produced in the second region is relatively greater than a loss produced in the first region, with respect to a high frequency component of an electric signal propagated through the signal electrode. As a result a wider modulation bandwidth can be realized.