NOVELTY - The method involves performing partial oxidation reaction process by hydrocarbon compound gas and oxygen-containing gas, and heating up a catalyst layer of a steam reforming reactor with reaction heat. The water vapor is introduced in addition to hydrocarbon compound gas and oxygen-containing gas, such that auto-thermal reforming reaction is occurred to heat catalyst layer with reaction heat. The steam reforming process is performed to perform steam reforming reaction by hydrocarbon compound gas and water vapor.    USE - Operating method of steam reforming reactor of steam reforming reaction apparatus used in fuel cell power generating device (all claimed).    ADVANTAGE - The activity is maintained stably over long term depending on specific use environment, even if the catalyst for steam reforming weak in the atmosphere in which oxygen exists. Since partial oxidation reaction process and auto-thermal reforming reaction process are performed before performing steam reforming reaction in the steam reforming reactor, temperature rising operation of the steam reforming reactor is efficiently performed using the oxidation reaction. The steam reforming reactor is started rapidly. Since the heated-up catalyst for steam reforming is active high thing containing ruthenium, the steam reforming reaction is performed still highly actively.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a steam reforming reaction apparatus has a hydrocarbon compound gas supply section which supplies hydrocarbon compound gas to the catalyst layer. An oxygen-containing gas supply section supplies oxygen-containing gas. A water vapor supply unit supplies water vapor to burn combustible gas discharged from the steam reforming reactor. A combustion unit heats the steam reforming reactor having the catalyst layer with catalyst for steam reforming as main component which makes to carry ruthenium and rhodium. A control apparatus controls the amount of each gas supplied from the hydrocarbon compound gas supply section, oxygen-containing gas supply section, and water vapor supply unit, so that the steam reforming process is performed for performing steam reforming reaction by hydrocarbon compound gas and water vapor. The catalyst for steam reforming makes the support having an alumina as a main component of 0.01-0.1 mass times of content of ruthenium. The catalyst for steam reforming makes the support to carry ruthenium by carrying out a hydrazine reduction, after impregnating ruthenium compound to the support.    DESCRIPTION OF DRAWING(S) - The drawing shows a graph illustrating the start-stop test pattern. (Drawing includes non-English language text)