A single-pipe cylinder-type reformer includes a plurality of circular cylinders standing upright coaxially and forming therebetween a zigzag gas flow path allowing a raw material gas to flow therein, a radiation cylinder coaxially arranged inside the plurality of circular cylinders, a burner arranged at one end of a center of the radiation cylinder for generating a combustion gas, a reforming catalyst layer obtained by packing with a reforming catalyst at least a first gas flow path section of the gas flow path closest to the burner. A metal pre-heat layer formed on an upstream side of the reforming catalyst layer is packed with a metal packing. Helical dividing means are provided in each gas flow path section of the gas flow path to extend in the axial direction of the circular cylinders. The helical dividing means helically divide a gas and make it flow through the first gas flow section.