An optical modulator includes a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a modulation part which modulates light waves propagating through the optical waveguide, and a light receiving element which detects the light waves propagating through the optical waveguide. As the modulation part, a first modulation part and a second modulation part, which respectively modulate light waves into which input light branches, are provided. As the light receiving element, a light receiving element for the first modulation part and a light receiving element for the second modulation part are provided. The light receiving elements are disposed such that their positions in a light propagation direction are shifted from each other by an amount corresponding to one light receiving element, or more.