In an optical modulator according to the present invention, a Mach-Zehnder optical waveguide is formed on a substrate having an electro-optic effect, a signal electrode and an earth electrode are disposed along a pair of branching waveguides of the optical waveguide, and an electric signal is applied on the signal electrode to thereby modulate a light being propagated through the optical waveguide. At this time, a first region and a second region are set in an interacting portion where the light and the electric signal interacts to each other, to form a polarization inversion region in each of the set regions, and also, an arrangement pattern of the signal electrode is determined so that a modulation direction in each of the set regions is opposite to each other. As a result, it is possible to realize the optical modulator of simple configuration capable of realizing simultaneously the broad modulation band and the wavelength chirping suppression.