NOVELTY - Steam-reforming fuel processing apparatus (1) for the production of hydrogen for feeling a fuel cell electric power generator, is structured as a single shell-and-tube heat exchanger comprising a tube-side portion and a shell-side portion, where the tube-side portion comprises tubes to which, through a first inlet (2a,2b), a predetermined flow of water and of a first hydrocarbon-based fuel may be fed, and which is fluidically connected to a first outlet (5); and a mixing chamber (8), provided with a porous septum (9).    USE - In the production of hydrogen for feeling a fuel cell electric power generator (claimed).    ADVANTAGE - The apparatus provides fuel processing by steam reforming entailing operating conditions that are, in the light of the thermal and mechanical resistance of the materials employed, less stressing for the latter, with a consequently reduced or null need to resort to special steels with higher properties but significantly more expensive, ensuring at the same time a reduced weight and encumberment, with reduced thermal dispersion and keeping unchanged, with respect to conventional solutions, the yields and degree of conversion in the very reactor. The innovative structure of the apparatus for fuel processing by steam reforming which operationally couples different portions of the apparatus itself thus promoting the thermal integration of distinct phases of the process leads consequently to an increased overall efficiency with respect to embodiments known in the art. There is reduced number of distinct components forming the apparatus and, consequently, also the overall encumberment of the apparatus is reduced. From the mechanical viewpoint, further, the fact of working at lower temperatures or, however, with a more efficient carry-out of the heat from the apparatus sections which are thermally more stressed, and which is efficiently used again in other portions of the apparatus, results in lesser thermal stresses in particular at the most critical spots, such as weldings.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of the steam reforming fuel processing apparatus.    Steam-reforming fuel processing apparatus (1)    First inlet for water and fuel (2a,2b)    First outlet (5)    Mixing chamber (8)    Porous septum (9)