To provide an apparatus for the performance assessment of a porous steam reformer which is capable of making a highly accurate assessment of the reforming performance of a porous steam reformer built in the stack of a fuel cell as an internal reformer.

The apparatus is made up of the lower apparatus part 1 in which a porous steam reformer S is placed on the bottom 3, a weight plate 8 which is placed on the top of the porous steam to cover the top with its flat bottom, and applies a specific pressure on the porous steam reformer, mixed gas feed paths 5 and 6 which introduce a mixed gas of hydrocarbon gas and steam into the porous steam reformer S form the center of the bottom 3 of the lower apparatus part 1, heating means 9a and 9b which indirectly heat the porous steam reformer at a temperature not lower than the reforming temperature, and temperature sensing means 10a-10c which are installed in the lower apparatus part 1 and measure temperatures at more than one position from the center to the periphery of the porous steam reformer.