In an optoelectronic conversion header, a ferrule holds an optical waveguide in a predetermined position so that an end face of the optical waveguide protrudes from an mounting surface of the ferrule. An electric wire is provided on the mounting surface of the ferrule, a optical semiconductor device is mounted on the mounting surface of the ferrule and electrically connected to the electric wire. From the end face of the optical waveguide, an optical signal is transferred in a transfer direction and the mounting surface of the ferrule is so arranged as to be deviated two degrees or more from a plane vertical to the transfer direction.