An optical waveguide device serving as a planar lightwave circuit, and an optical waveguide device which enables an attempt to realize greater functionality as a planar optical waveguide device. An optical waveguide device is configured to have a first cladding layer, a core formed on the first cladding layer for guiding light, and a second cladding layer formed on the first cladding layer and the core so as to surround the core, wherein the core comprises a trunk portion constituting a body of the core and a layered structure portion essentially perpendicular to a plane forming the first cladding layer.