NOVELTY - A single pipe cylindrical reformer has a vertical cylindrical outer tube, a cylindrical inner tube inside the outer tube and arranged coaxially, cylindrical intermediate tubes between the inner and outer tubes and arranged coaxially, cylindrical radiating tube inside the inner tube and arranged coaxially, a burner fixed to an axial end part of the reformer by arranging coaxially in the radiating tube, and circulating flow passages formed in radial direction layers between the inner tube and the intermediates tubes and between the intermediate tubes and the outer tube so reforming catalyst can be packed as a reforming catalyst layer in at least one part.    USE - The reformer produces hydrogen-rich reformed gas by steam reforming hydrocarbon fuels such as city gas, natural gas and LPG, and alcohols, and can be combined with solid polymer fuel cells.    ADVANTAGE - The reformer is small in size, quick starting and has a high operating efficiency. A reformed gas of low carbon monoxide concentration is produced.    DETAILED DESCRIPTION - The fixing position of the burner is a double-bottom structure which is sealed by a cover plate which separates both axial end parts of the opposing outer and inner tubes by a fixed distance. An INDEPENDENT CLAIM is also included for the operation method of the single-pipe cylindrical reformer.    DESCRIPTION OF DRAWING(S) - Figure 3 shows a detailed cross-section of the single-tube cylindrical reformer.    Cylindrical Outer Tube (10)    CO Modification Catalyst Layer (11)    Selective Oxidation catalyst Layer (12)    Reforming catalyst Layer (13)    Cylindrical Radiating Tube (14)    Cover (16)    Burner (18)    Steam Production Port (20)    Steam Production Port (21)    Water Supply Port (22)    Combustion Exhaust Gas Outlet (24)    Supply Port of reformed Raw Gas and Steam (26)    Reformed Gas Production Port (28)    Air Supply Port (30)    Steam Generator (34)    Separation Wall (35)    Air Passage (42)    Air Introduction Hole (43)    Oxidation Catalyst Layer (44)    Air Mixture Layer (46)    Cooling Medium Passage (48)    Heat Insulating Layer (49)    Heat Recovery Layer (50)    Cylindrical Intermediate Tubes (60)    Outer Intermediate Tube (61)    Second Intermediate Tube (62)    Third Intermediate Tube (63)    Fourth Intermediate Tube (64)    Fifth Intermediate Tube (65)    Sixth Intermediate Tube (66)    Seventh Intermediate Tube (67)    Inner Intermediate Tube (68)    Base (71)    Base Plate (76)    Base Plate (78)    Reformer (81)    Solid Polymer Fuel Cell (100)    Fuel Gas Supply Tube (102)