PURPOSE: To prevent the damages of a burner and a fire-resistant heat-insulating material, etc., with flames having abnormal high temperatures by stationarily partially oxidizing a hydrocarbon in a combustion chamber, and to prevent the deterioration, etc., of a catalyst for the second reforming and enhance the reaction degree of the second reforming by feeding a gas having a uniform temperature and a homogeneous composition to a second reforming catalyst layer.

CONSTITUTION: A heat-insulating type hydrocarbon single container reactor used for subjecting the gas mixture of a hydrocarbon with steam to the first reforming reaction, partially oxidizing the first reformed product with an oxygen-containing gas, subjecting the partially oxidized product to the second reforming reaction, and using the obtained high temperature gas as a heating source for the first reforming reaction is characterized by disposing the oxygen gas-containing gas-blowing nozzle 14 of the combustion chamber at the center of the gas-blowing nozzle 13 for the first reforming, and allowing the first reformed gas and the oxygen-containing gas to upward flow in parallel to each other for the partial oxidation.