An optical waveguide device includes: a substrate having an electro-optical effect; an optical waveguide formed on the substrate; and a control electrode for applying an electric field to the optical waveguide. The optical waveguide device has the following characteristics. A thickness of the substrate is 30 μm or less. The control electrode has a signal electrode and a ground electrode. A low-permittivity layer is formed at least on a surface portion of the signal electrode in contact with the substrate.