An optoelectric composite substrate of the present invention includes an insulating film, an optical waveguide embedded in the insulating film in a state that an upper surface is exposed from the insulating film, a via hole formed to pass through the insulating film, a conductor formed in the via hole, and a connection terminal on which an optical device is mounted and which is connected to an upper end side of the conductor, wherein the connection terminal is embedded in an upper-side portion of the via hole or is projected from the insulating film.