In an optical modulator comprising substrate 1 having electro-optical effect, two optical waveguides 3a, 3b formed in the substrate, buffer layer 2 formed on the substrate, traveling-wave electrode 4 having center conductor 4a and ground conductors 4b, 4c above the buffer layer, and ridge sections formed with recessed sections 9a to 9c by carving at least a part of the substrate where an electrical field strength of high-frequency electrical signal propagating the traveling-wave electrode is strong, in which the ridge sections include center conductor ridge section 8a having the center conductor formed above and ground conductor ridge section 8b having the ground conductor formed above, and the center conductor ridge section has one of the two optical waveguides formed therein, the recessed sections are practically symmetrical to the center line between the two optical waveguides and the traveling-wave electrode is practically symmetrical to the center line of the center conductor.