An optical device includes a substrate, a plurality of optical elements formed in an element formation region of the substrate, a plurality of lenses formed over the element formation region so as to correspond to the plurality of optical elements, and a protective layer formed so as to cover the plurality of lenses. A holding member is formed on the protective layer in a region outside the element formation region. The holding member holds a bottom surface of a transparent member. A gap between the protective layer and the transparent member is filled with an adhesive.