An electric connector portion, an optical element and a mounting board formed with a circuit executing a predetermined signal conversion and relay processing are held by a case. The case includes an optical element-containing recessed portion having electrical conductivity, and the optical element is arranged in the optical element-containing recessed portion. Further, the case may include a mounting part-containing recessed portion independently from the optical element-containing recessed portion, and mounting parts on the mounting board may be arranged in the mounting part-containing recessed portion.