Abstract: A hydrocarbon-reforming reactor by a steam reforming reaction and a partial oxidation reaction, which comprises a chamber for feeding oxygen-containing gas, a chamber for feeding a mixture gas of hydrocarbon with steam and a chamber for heat exchange of reformed gas in this order from one side of the reforming reactor, and which further comprises a catalyst layer filled in a space between an inner tube having an opening to the chamber for feeding oxygen-containing gas and a reaction tube being so placed as to position the inner tube in its middle portion and having an opening to the chamber for feeding the mixture gas, anda process for producing reformed gas from hydrocarbon which comprises carrying out a steam reforming reaction in the catalyst layer on the side of the chamber for feeding the mixture gas of hydrocarbon with steam by feeding the mixture gas of hydrocarbon with steam to the catalyst layer from the chamber for feeding the mixture gas, carrying out a partial oxidation reaction and steam reformin