In a regenerator for an absorption refrigerating machine which uses combustion gas as a heat source, the regenerator comprises a plurality of drum shells provided in a body casing of the regenerator, each drum shell has a solution inlet provided in a shell part of the drum shell, a solution outlet having an overflow structure and provided in the shell part at a position lower than the solution inlet, a vapor outlet provided in the shell part at a position higher than the solution inlet, a multiplicity of heat transfer fins provided on an outer periphery of a shell part of the drum shell and a circulation guide provided along an inner periphery of the shell part, the plurality of drum shells may be arranged in a side by side parallel and/or in an up and down series relationship to increase the capacity of the regenerator by proportional design.