An optical waveguide device increases the intensity of light transmitted through an optical waveguide for a reduced cost without expanding the area of the light. The optical waveguide device according to the present invention includes an optical waveguide and defining surfaces defining the optical waveguide. The defining surfaces are formed of plasmon activating medium. The defining surface include a pair of inner parts that face each other along a direction perpendicular to a light transmission direction. The distance between the inner parts is less than the half of the wavelength of the light transmitted through the optical waveguide.