An optical modulator includes a substrate on which an optical waveguide and a modulation electrode that modulates a light wave propagating through the optical waveguide are formed, and a case housing the substrate, the optical waveguide includes at least an optical branching part that branches one light wave into two light waves or an optical combining part that combines two light waves into one light wave, the modulation electrode has a signal electrode and a ground electrode, and a part of the signal electrode is disposed so as to cross the optical branching part or the optical combining part, and the optical modulator is provided with a suppressing unit that suppresses changes in an intensity ratio of the light waves branched at the optical branching part or an intensity ratio of the light waves combined at the optical combining part, by the signal electrode.