A carbon-dioxide-gas absorber includes a main component of composite oxide, the composite oxide including Ti and X that is at least one of Sr and Ba, and the composite oxide having a molar ratio (X/Ti) of about 1.8 to about 2.2. A substance having a perovskite structure and an (X/Ti) of about 0.9 to about 1.1 or at least one selected from green sheets, green sheet wastes, green-sheet-laminate wastes, and precursors of green sheets including the substance is fired with at least one of strontium carbonate and barium carbonate. An apparatus includes a carbon-dioxide-gas-absorbing mechanical unit that allows a carbon-dioxide-gas absorber to absorb a carbon dioxide gas at about 1.0×104 to about 1.0×106 Pa and at about 500° C. to about 900° C.; and a carbon-dioxide-gas-evolving mechanical unit that evolves the absorbed carbon dioxide gas at about 1000 Pa or less and at at least about 750° C.