NOVELTY - A modification unit (300) has modifier (620), carbon monoxide-modifying device (820) and carbon monoxide selective oxidation device (830), each having case component (610) having heat insulation portion (500) at outer surface. The edge portion of insulation portion is held by holding unit (812) during protrusion of insulating portion from one end portion of case. Modifier produces hydrogen gas-containing reformed gas by heating source gas containing hydrocarbon material. Device (830) carries out oxidation of carbon dioxide and carbon monoxide remained in reformed gas.    USE - Modification unit is used for fuel cell system (claimed).    ADVANTAGE - The modification unit has stable modification efficiency and simple structure.    DETAILED DESCRIPTION - A modification unit (300) has a modifier (620), carbon monoxide-modifying device (820) and carbon monoxide selective oxidation device (830), each having a cylindrical case component (610) having a heat insulation portion (500) at outer peripheral surface. The edge portion of heat insulating portion is held by a holding unit (812) during protrusion of insulating portion in outward direction from one end portion of case component. The modifier produces hydrogen gas-containing reformed gas by heating a source gas containing a hydrocarbon raw material in the presence of a modification catalyst, using combustion gas of burner. The carbon monoxide-modifying device modifies carbon monoxide contained in reformed gas to carbon dioxide in the presence of modification catalyst. The carbon monoxide selective oxidation device carries out oxidation of carbon dioxide produced by modification device, and carbon monoxide remained in reformed gas by selective oxidation catalyst.    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of modification unit.    Modification unit (300)    Heat insulating portion (500)    Case (610)    Modifier (620)    Holding unit (812)    Carbon monoxide modifier device (820)    Carbon monoxide selective oxidation device (830)