Electrochemical compound device has been developed. Tantalum electrolytic rectifier is combined with an accumulator. Tantalum electrode of the rectifier has an oxidized film Ta_2O_5 metamorphosed by heating treatment. The positive pole of an accumulator is used as the cathode of tantalum electrolytic rectifier and the electrolytic solution of an accumulator is directly used as the electrolytic tolution of tantalum rectifier. When the negative pole of an accumulator is used as the cathode of tantalum rectifier, the specific gravity of electrolytic solution, and the electromotiveforce of an accumulator are decreased.