NOVELTY - The fuel reformer (1) has carbon dioxide adsorption desorption chambers (20,21) divided by a dividing wall (32), and modification chambers (22,23) having modification route and exhaust gas route divided by the dividing wall. The chambers (20,21) contain porous metal coated with adsorption agent for adsorbing carbon dioxide from exhaust gas at low temperature and desorbing at high temperature.    USE - For engine system (claimed) for modifying natural gas.    ADVANTAGE - The fuel reformer has improved sealing performance, and is simple and compact. The reformer modifies the natural gas efficiently, and improves the thermal efficiency of engine system.    DETAILED DESCRIPTION - The fuel reformer (1) has carbon dioxide adsorption desorption chambers (20,21) divided by a dividing wall (32), and modification chambers (22,23) having modification route and exhaust gas route divided by the dividing wall. The chambers (20,21) contain porous metal coated with adsorption agent for adsorbing carbon dioxide from exhaust gas at low temperature and desorbing at high temperature. The chambers (20,21) have low temperature exhaust gas route and high temperature exhaust gas route formed by arranging the porous metal. The modification route of chamber (22) is formed by catalyst chamber in which natural gas and carbon dioxide are reacted in presence of catalyst (I) coated with porous metal, and natural gas is converted into modified fuel. The exhaust gas route contains porous metal. The modification route of chamber (23) is formed by catalyst layer in which natural gas and water vapor are reacted in the presence of catalyst (II) coated with porous metal using water vapor from outside. The chamber (23) is arranged at the downstream of the chamber (22). The modified fuel is supplied to the engine (2).    An INDEPENDENT CLAIM is included for engine system.    DESCRIPTION OF DRAWING(S) - The figure shows the fuel reformer integrated in the engine system.    fuel reformer (1)    engine (2)    carbon dioxide adsorption desorption chambers (20,21)    modification chambers (22,23)    dividing wall (32)