It was found that hydrogen recovery in a palladium membrane reactor is depressed by the back-permeation of hydrogen from the perm-side to the reforming side near the inlet of the reactor, where the partial pressure of hydrogen on the reforming side is lower than that of the perm side because the reaction has just started. To diminish this phenomenon, three methods, (1) use of a sweep gas, (2) premixing hydrogen into the feed, and (3) extension of the catalyst bed, were examined by simulation as well as experimentally. As a result, it was shown that the first method, if one uses steam as the sweep gas, is useful in a fuel cell system requiring humidified hydrogen. The second one is not as effective because the hydrogen amount recovered is less than that premixed. The third one is the best for obtaining pure hydrogen.