NOVELTY - A modifier (A) has cylindrical container (1) provided at the center part, cylindrical 1st outer wall (2) provided at the inner side annular space on the outer side of the cylindrical container, cylindrical 2nd outer wall (3) provided at the outer side annular space at the outer side of the cylindrical 1st outer wall, and spiral tubes (9) provided at the outer side annular space between 1st outer wall and 2nd outer wall.    USE - Modifier for producing hydrogen rich reducible gas used in fuel cell systems (claimed).    ADVANTAGE - Size is reduced, heat exchange and heating efficiency are improved, and manufacturing and operation costs are reduced.    DETAILED DESCRIPTION - A modifier (A) has cylindrical container (1) provided at the center part, cylindrical 1st outer wall (2) provided at the inner side annular space on the outer side of the cylindrical container, cylindrical 2nd outer wall (3) provided at the outer side annular space at the outer side of the cylindrical 1st outer wall, and spiral tubes (9) provided at the outer side annular space between 1st outer wall and 2nd outer wall. The inner side annular space between the cylindrical container and 1st outer wall is a turning flame type combustion part (T) which goes to the center axis direction while combustion gas turns. The inside of the spiral tubes provided at the outer side annular space between 1st outer wall and 2nd outer wall is a steam generating part (U) which evaporates the water supplied in a pipe with the heat from the inside combustion part and generates water vapor. Helical space parts other than the spiral tubes at the outer side annular space are mixing pre-heating parts (V) which mixes the water vapor produced by spiral tubes and hydrocarbon raw fuel introduced into the space part and pre-heats with the heat from the inside combustion part. The inside of cylindrical container is a modification part (S). While filling with modification catalyst, an internal modification catalyst is heated by the heat from the outside combustion part. The mixed gas of water vapor and raw fuel which were pre-heated and introduced in the mixing pre-heating part is modified by allowing to pass through the heated modification catalyst. Hydrogen rich reducible gas is produced reformed gas. An INDEPENDENT CLAIM is included for fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the fuel cell system. (Drawing includes non-English language text).    Cylindrical container (1)    1st outer wall (2)    2nd outer wall (3)    Spiral tubes (9)    Modifier (A)    Modification part (S)    Combustion part (T)    Steam generating part (U)    Mixing pre-heating parts (V)