Abstract: An active metal bed provided with a filter unit of sintered metal having a wide surface in the horizontal direction, enclosing an active metal powder running a reversible hydrogenation reaction therein and, which is single or plural combined in series, a heater attached thereto and an airtight container housing them, and characterized by, at the time of absorbing hydrogen isotope gas, contacting or flowing the gas to the active metal through the filter, while preventing the scattering of active metal powder, to obtain a large hydrogen absorption velocity by a wide gas contacting area and a decreased pressure loss at the time of gas flowing, and characterized by, at the time of releasing hydrogen isotope gas, preventing the overheating of air tight container and the permeating of hydrogen thereby while heating only the filter unit by the heater.