A single-pipe cylinder type reformer of the invention includes a plurality of circular cylinders standing upright coaxially, a radiation cylinder coaxially arranged inside the plurality of circular cylinders, and a burner arranged at one end of the center of the radiation cylinder, and has a reforming catalyst layer obtained by packing with a reforming catalyst at least a first gas flow path closest to the burner among a plurality of gas flow paths divided by the plurality of circular cylinders and having annular cross-sections. A pre-heat layer formed on one end side (upstream) of the reforming catalyst layer packed with the reforming catalyst is packed with a metal packing. Helical dividing means are provided in the respective gas flow paths to extend in the axial direction of the circular cylinders. The helical dividing means helically divide a gas and makes it flow through the first gas flow path.
