An optical waveguide device including: an optical waveguide composed of a protruding portion extending on a substrate; a signal electrode that is formed on the substrate and controls light waves propagating through the optical waveguide, in which the optical waveguide includes a Mach-Zehnder optical waveguide including two parallel waveguides having curved portions, the signal electrode includes two signal lines for transmitting a differential signal, respectively intersecting the two parallel waveguides at the curved portions, and in an intersection region, which is a region on the substrate where the two signal lines and the two parallel waveguides intersect, at least one of the two signal lines has a signal propagation velocity faster than in a portion other than the intersection region or one of the two signal lines has a signal propagation velocity faster than an other signal line.