NOVELTY - Hydrogen is generated by reforming a hydrocarbon fuel in a fuel reformer by an exothermic catalytic partial oxidation process to hydrogen, converting the generated hydrogen into water steam that is fed back into the fuel reformer, initiating an endothermic catalytic steam reforming process in the fuel reformer by the water steam, and feeding hydrogen to the fuel cell.    USE - For generating hydrogen for operating a fuel cell for e.g. aircrafts, ships and vehicles.    ADVANTAGE - The inventive method can be started and operated reliably under freezing ambient temperature conditions without using anti-freezing agents in a water supply.    DETAILED DESCRIPTION - Generation of hydrogen comprises reforming a hydrocarbon fuel in a fuel reformer by an exothermic catalytic partial oxidation process to hydrogen; converting the generated hydrogen into water steam that is fed back into the fuel reformer; initiating an endothermic catalytic steam reforming process in the fuel reformer by the water steam, so that by the combination of exothermic and the endothermic processes an autothermal fuel reforming process (ATR) is created; and feeding hydrogen that is generated by the ATR process, to the fuel cell. INDEPENDENT CLAIMS are also included for:    (1) arrangement for reforming a hydrocarbon fuel, comprising a fuel reformer (1) containing an oxidation catalyst (1a), for generating hydrogen from supplied fuel and oxygen; and a catalytic combustion reactor (3), for catalytically converting hydrogen into water steam, where the fuel reformer and the combustion reactor are connected in a loop so that by the water steam from the combustion reactor an autothermal fuel reforming process can be created in the fuel reformer;    (2) control unit for controlling the arrangement;    (3) fuel cell system for generating power by fuel cell, comprising the arrangement;    (4) computer program comprising computer program code adapted to perform a method when the program is on a programmable microcomputer; and    (5) computer program product stored on a computer readable medium, comprising the computer program code.    DESCRIPTION OF DRAWING(S) - The figure is a block diagram of the arrangement for presenting a first stage of the start-up phase of the inventive method.    Fuel reformer (1)    Oxidation catalyst (1a)    Gas clean-up reactor (2)    Catalytic combustion reactor (3)    Pipe (5a)