NOVELTY - A fuel reforming system has a membrane reactor with a reforming catalyst section (4), membrane hydrogen separator (5), hydrogen passage, and combustion catalyst section (3); first supply device; second supply device; sensor (16, 17); and controller (15).    USE - For use as fuel reforming system (claimed), e.g. in a fuel cell.    ADVANTAGE - The novel system avoids hydrogen embrittlement at low temperatures.    DETAILED DESCRIPTION - The fuel reforming system comprises a membrane reactor with a reforming catalyst section, for reforming a supplied fuel gas into a reformate gas, a membrane hydrogen separator, for separating hydrogen from the reformate gas, a hydrogen passage, for transferring hydrogen separated by the separator to a fuel cell, and a combustion catalyst section, for heating the reforming catalyst section; first supply device; second supply device; sensor; and controller. The first supply device supplies combustion gas to the membrane reactor, and has a combustor for producing the combustion gas. The second supply device supplies fuel gas to the reforming catalyst section. The sensor detects temperature of the membrane hydrogen separator. The controller determines whether or not the temperature of the separator is at least equal to a target temperature before the reforming catalyst section starts reformate reactions on the fuel gas; to command the first supply device to supply the combustion gas to one of the reforming catalyst section and hydrogen passage when the temperature is smaller than the target temperature; and to command the first supply device to stop the supply of gas and command the second supply device to start supply of the fuel gas to the reforming catalyst section when the temperature reaches the target temperature.    An INDEPENDENT CLAIM is also included for a startup control method, for use in the above fuel reforming system, by determining whether or not the temperature of the separator is at the target temperature; commanding the first supply device to supply the combustion gas when the temperature is smaller than the target temperature; and commanding the first supply device to stop the supply of the gas and commanding the second supply device to supply the fuel gas when the temperature reaches the target temperature.    DESCRIPTION OF DRAWING(S) - The figure shows the above fuel reforming system.    Combustion catalyst section (3)    Reforming catalyst section (4)    Membrane hydrogen separator (5)    First, second, and third passages (8,10,12)    First, second, and third valves (9,11,13)    Sensors (16, 17)