The invention provides an optical device that enables a mutual electrical connection between the stacked semiconductor substrates to be realized with ease and high reliability and to provide for miniaturization. The optical device has a first semiconductor substrate having an optical part and a first pad, a second semiconductor substrate having an integrated circuit and a second pad which is stacked under the first semiconductor substrate, a through-hole continuously extending through the first and the second semiconductor substrate, and a conductive part so formed as to include the inside of the through-hole.