The present invention provides a cost-saving and space-saving optical modulator enabling application of modulation signals with high phase difference accuracy without using a separate component for generating a phase difference outside of the optical modulator, when identical modulation signals having a predetermined phase difference are applied into a plurality of modulation electrodes.An optical modulator 20 including a substrate with an electro-optic effect, a plurality of optical waveguide sections 10 formed on the substrate, and a plurality of modulation electrodes 21 and 22 for modulating lights passing through the optical waveguide sections, and into which identical modulation signals having a predetermined phase difference are applied, wherein a branch element for branching a modulation signal into a plurality of modulation signals is formed, and a delay line for generating the phase difference is formed in the middle of lines for applying the modulation signals branched by the branch element into the plurality of modulation electrodes.