A reformer for reacting a raw material gas to be reformed, with an oxidizing agent gas and a reforming agent gas in the presence of an oxidation catalyst and a reforming catalyst to obtain a hydrogen-containing gas, including: a set of catalyst layers consisting of an oxidation catalyst layer and a reforming catalyst layer, and two or more inlets for feeding the oxidizing agent gas to the oxidation catalyst and/or the reforming catalyst in plural stages. The reformer can produce a hydrogen-containing gas without forming a combustion region of a temperature of as high as one thousand and several hundreds centigrade and can be manufactured at a low cost.