Provided is a monolithic integrated composite device including: a silicon substrate which is partitioned into a silicon integrated circuit forming region and a silicon optical device forming region; a buried oxide layer which is formed locally in the silicon substrate of the silicon optical device forming region and isolates unit devices of the silicon optical device forming region; an overlay layer formed locally on the buried oxide layer; a silicon optical device formed in the silicon optical device forming region using the silicon overlay layer; a silicon integrated circuit formed in the silicon integrated circuit forming region of the silicon substrate; and wiring connecting the silicon integrated circuit and the silicon optical device or connecting the silicon optical devices or connecting the silicon integrated circuits.