NOVELTY - Hydrogen-containing-gas production apparatus has conversion part for converting carbon monoxide gas in reforming process gas, from modification part (4), into carbon dioxide gas. Piping (45, 46) for mixed gas supplies oxygen-containing gas and the reforming process gas discharged from the conversion part to selective-oxidation part in a mixed state. It is formed so that unification path part which has pipe-with-collector path part (47b) is connected in orthogonally crossed with respect to main-line part (47a). The oxygen-containing gas may flow through the pipe-with-collector path part.    USE - For producing hydrogen-containing gas useful as fuel of fuel cell of solid polymer type.    ADVANTAGE - The apparatus is capable of suppressing the change of the mix ratio of the reforming process gas and oxygen-containing gas which are supplied to the selective-oxidation part.    DETAILED DESCRIPTION - Hydrogen-containing-gas production apparatus comprises a reforming part for producing reforming process gas having hydrogen gas as a main component by carrying out reforming processing of the raw materials and mineral fuel of a hydrocarbon group using steam. A conversion part performs conversion processing of carbon monoxide gas in the reforming process gas into a carbon dioxide gas. A selective-oxidation part performs selective-oxidation processing of the carbon monoxide gas supplied from the conversion part into carbon dioxide using oxygen-containing gas. Piping for mixed gas supplies oxygen-containing gas and the reforming process gas discharged from the conversion part to the selective-oxidation part in a mixed state. The piping has a linear main-line part, and pipe-with-collector path part connected in the state orthogonally crossed with respect to the main-line part. It is formed so that the unification path part is provided. The reforming process gas is made to flow through the main-line part. The oxygen-containing gas may be made to flow through the pipe-with-collector path part.    DESCRIPTION OF DRAWING(S) - The figure is a partly notched front view of a hydrogen-containing-gas production apparatus.    Modification part (4)    Piping (45, 46)    Main-line part (47a)    Pipe-with-collector path part (47b)