Effective utilization of biogas can contribute to the reduction of greenhouse gasses and the promotion of recycling. However, further development of gas storage technology is required. In this study, focused on adsorption storage technology and evaluated the storage density of biogas taking into account of temperature rise of the activated carbon. First, methane and carbon dioxide adsorption isotherms of various activated carbons were determined and analyzed by the Toth equation and the extended Toth equation. Secondly, binary adsorption equilibria of methane and carbon dioxide were measured and analyzed with IAST (ideal adsorbed solution theory). The amount adsorbed of the digestion gas from an institution and that predicted by IAST for digestion gas of the same composition were in good agreement, demonstrating that IAST is able predict the storage capacity of digestion gas. Finally, the adsorption storage density of digestion gas taking into account of the influence of adsorption heat was calculated by adiabatic approximation, and a temperature rise of 32K for storage of digestion gas at 0.7MPa in activated carbon A. However, storage capability was 10 (0.5MPa) to 16 (0.2MPa) times higher than the conventional compressed storage at same pressure. Furthermore, the temperature rise predicted by the proposed method agreed within 3K with the temperature rise measured with the pilot-scale equipment.