An optical waveguide device expands the operable frequency range toward the higher frequency side. The device includes a single-mode optical resonator waveguide serving as an optical ring resonator, a single-mode optical input/output waveguide located close to the resonator waveguide in an area, and a Mach-Zehnder interferometer formed in such a way as to include a part of the resonator waveguide as its first optical waveguide arm and a part of the input/output waveguide as its second optical waveguide arm in the area. The interferometer has a first optical coupler for optically coupling the first and second waveguide arms with an input-side part of the input/output waveguide and a remaining part of the resonator waveguide due to multiple-mode optical interference, and a second optical coupler for optically coupling the first and second waveguide arms with an output-side part of the input/output waveguide and the remaining part of the resonator waveguide due to multiple-mode optical interference.