An optical modulator includes: a substrate that having an optical waveguide that includes a split section that splits light into two light waves, a pair of arms through which the light waves propagate, and a combining section that combines the light waves from the pair of arms with each other; and an electrode that overlaps part of the optical waveguide and generates an electric field by a voltage applied to the electrode. The optical waveguide has a narrow portion that is narrower than another portion of the optical waveguide and is arranged so that the electrode does not overlap with the narrow portion.