An optical device includes: a substrate including plural waveguide cores; and an optical component provided on the substrate, the optical component including plural lenses, each of the plural lenses transmitting light passing through one of the corresponding plural waveguide cores on the substrate. The substrate and the optical component are each provided with a positioning structure. The positioning structure includes plural protrusions and plural recesses provided on the substrate and the optical component. Each of the plural recesses accommodates a corresponding one of the plural protrusions, and an outer surface of each of the plural protrusions contacts a positioning surface of a corresponding one of the plural recesses. The positioning surface is a part of an inner surface of each of the plural recesses having accommodated the corresponding one of the plural protrusions to position the plural lenses relative to the substrate.