NOVELTY - Hydrocarbon-type fuel is reformed with water vapor. Carbon monoxide (CO) gas in reformed gas (RG) is transformed into carbon dioxide gas. CO gas still remaining in the RG is oxidized by a gas (A) in an oxidation portion (9). The supply of fuel to the reforming portion is stopped to stop the hydrogen-containing gas producing apparatus. The supply of gas (A) is continued. Residual gas remaining in the oxidation portion is extruded.    USE - Used for stopping a hydrogen-containing gas producing apparatus (claimed) used for producing hydrogen-containing gas which is used as fuel gas for electric power generation in fuel cells such as solid polymer electrolyte-type fuel cells.    ADVANTAGE - An increase in concentration of carbon monoxide in hydrogen-containing gas at the time of shutdown and start up period is prevented, and hence requirement of maintenance of hydrogen-containing producing apparatus is reduced. Oxidation of selective oxidation catalyst by oxygen-containing gas is suppressed, and reduction in activity of the selective oxidation catalyst is also prevented.    DETAILED DESCRIPTION - Hydrocarbon-type fuel is reformed with water vapor in a reforming portion (6), and a gas containing hydrogen gas as the main constituent is obtained. Carbon monoxide gas contained in the reformed gas is transformed into carbon dioxide gas in a transforming portion (7). Carbon monoxide gas which still remains in the reformed gas even after transformation, is selectively oxidized by oxygen-containing gas in a selective oxidation portion (9), and carbon dioxide is obtained. The supply of fuel to the reforming portion is stopped to stop running of hydrogen-containing gas producing apparatus, whereas the supply of oxygen-containing gas to selective oxidation portion is continued. A purge gas is subsequently supplied to the reforming portion, and residual gas remaining in the selective oxidation portion is extruded with the purge gas. The supply of oxygen-containing gas to the selective oxidation portion is stopped when the residual gas remaining in the selective oxidation portion is completely extruded and the selective oxidation portion is filled with purge gas.    An INDEPENDENT CLAIM is included for a hydrogen-containing gas producing apparatus. The hydrogen-containing gas producing apparatus has a fuel supplying device (V1), an oxygen-containing gas supplying device (V2), a purge gas supplying device (V10) and an operation controlling device (10). The fuel supplying device is switchable to a stop condition which stops the supply of fuel to the reforming portion. The oxygen-containing gas supplying device is switchable to a stop condition which stops the supply of oxygen-containing gas to the selective oxidation portion. The purge gas supplying device is switchable to a supplying state which supplies purge gas to the reforming portion, and to halt condition which stops supply of purge gas to the reforming portion. The purge gas supplying device controls the running condition of the hydrogen-containing gas producing apparatus. The fuel gas supplying device is switched to a stop condition, and the oxygen-containing gas supplying device is maintained in the supplying state, when the operation controlling device commands for shutdown of the apparatus. The purge gas supplying device is switched to the supplying state, and residual gas remaining in the selective oxidation portion is extruded with the purge gas. The purge gas supplying device is switched to a stop condition when the selective oxidation portion is filled with the purge gas after completely extruding residual gas in the selective oxidation portion.    DESCRIPTION OF DRAWING(S) - The figure shows block diagram of structure of the hydrogen-containing gas producing apparatus. (Drawing includes non-English language text).    Reforming portion (6)    Transforming portion (7)    Selective oxidation portion (9)    Operation controlling device (10)    Fuel supplying device (V1)    Oxygen-containing gas supplying device (V2)    Purge gas supplying device (V10)