NOVELTY - The fuel reformer (10) is equipped with modification fuel discharging unit (20), oxidizing agent gas supplying unit (A), fuel introduction chamber (B) (22), modifying catalyst and controlling unit (35). Hydrocarbon-type modification fuel is intermittently supplied to the modifying catalyst, and hydrogen is produced from the modification fuel using modification reaction.    USE - For producing hydrogen from hydrocarbon-type fuel, which is used for fuel cell of fuel cell system.    ADVANTAGE - The fuel reformer effectively prevents reduction of efficiency of modification reaction caused by precipitation of carbon on modification catalyst.    DETAILED DESCRIPTION - The fuel reformer (10) is equipped with modification fuel discharging unit (20), oxidizing agent gas supplying unit (A), fuel introduction chamber (B) (22), modifying catalyst and controlling unit (35). Hydrocarbon-type modification fuel is intermittently supplied to the modifying catalyst, and hydrogen is produced from the modification fuel using modification reaction. The unit (20) discharges modification fuel intermittently. The unit (A) discharges oxidizing agent gas containing oxygen when at least the unit (20) stops discharging modification fuel. The modification fuel and oxidizing agent gas are directly introduced into the chamber (B). A catalyst portion is connected and provided in the chamber (B), and has modification catalyst. The modification fuel and oxidizing agent gas are supplied to the catalyst portion. The control portion controls unit (A) to discharge oxidizing agent gas of quantity more than volume of chamber (B) whenever the unit (20) stops discharging modification fuel, and controls unit (20) to discharge modification fuel of quantity required for modification reaction.    An INDEPENDENT CLAIM is included for method of operating fuel reformer. Modification fuel is intermittently discharged to interior portion of fuel introduction chamber. The fuel is passed to modification catalyst which promotes modification reaction, and hydrogen is produced. Oxidizing agent gas of quantity more than volume of fuel introduction chamber is supplied to fuel introduction chamber when the discharge of modification fuel is stopped. Carbon precipitated on modification catalyst is oxidized and removed using the oxidizing agent gas.    DESCRIPTION OF DRAWING(S) - The figure shows the block diagram of structure of fuel cell system equipped with the fuel reformer. (Drawing includes non-English language text).    Fuel reformer (10)    Fuel cell system (15)    Fuel cell (17)    Modification fuel discharging unit (20)    Fuel introduction chamber (22)    Modifier (24)    Heat exchanger (26)    Carbon monoxide reducing unit (28)    Heating unit (30)    Controlling unit (35)