Abstract: An optical waveguide device includes: a substrate; an optical element arranged on the substrate; and an optical circuit part having an optical waveguide formed on the substrate. The optical circuit part includes: a core whose optical axis is matched with the optical element; and a dummy core arranged on a same layer to the core and exposed on a side being not opposed to the optical element when the optical element is arranged on the substrate. The relative position between the optical waveguide and the optical element can be recognized by observing the dummy core. The planar shape of the optical circuit has a convex portion. The width of the convex portion and the width of the optical element are same in the opposing edge face where the optical element and the core is opposed to one another.