NOVELTY - A fuel treating apparatus comprises modification part which produces reformed gas (22) containing hydrogen, carbon monoxide, and water vapor, denaturation part (4) in which carbon monoxide and water in reformed gas are made to react and in which carbon monoxide concentration is reduced, mixing part (5) which mixes air (23) containing oxygen and reformed gas, selective oxidation part (6) which makes carbon monoxide in reformed gas and oxygen react and produces fuel gas, reformed gas flow path (11) where reformed gas from denaturation part passes, and air flow path (12).    USE - A fuel treating apparatus for producing fuel gas (claimed) used for fuel cell systems, such as residential cogeneration system and power source system of mobile communication base station.    ADVANTAGE - Fuel gas with low carbon monoxide concentration can be produced, pressure loss of gas can be minimized, and the number of steps required to manufacture fuel gas can be reduced.    DETAILED DESCRIPTION - A fuel treating apparatus comprises modification part which produces reformed gas (22) containing hydrogen, carbon monoxide, and water vapor, denaturation part (4) in which carbon monoxide and water in reformed gas are made to react and in which carbon monoxide concentration is reduced, mixing part (5) which mixes air (23) containing oxygen and reformed gas, selective oxidation part (6) which makes carbon monoxide in reformed gas and oxygen react and produces fuel gas, reformed gas flow path (11) where reformed gas from denaturation part passes, air flow path (12) which conveys air supplied from air supply part and is connected to reformed gas flow path, mixing vessel (13) which is connected to reformed gas flow path and mixes reformed gas and air, and mixing header (14) which has annular space and has flow path (15) which conveys gas from mixing header to selective oxidation part. Mixing vessel has area of surface linked to reformed gas flow path which is larger than cross-sectional area of reformed gas flow path and hole (54) in side surface which serves as exit of gas. Normal line direction of surface with hole is not parallel to central axis (52) of annular space of mixing header.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the mixing part of the fuel treating apparatus. (Drawing includes non-English language text).    Denaturation part (4)    Mixing part (5)    Selective oxidation part (6)    Reformed gas flow path (11)    Air flow path (12)    Mixing vessel (13)    Mixing header (14)    Flow path (15)    Reformed gas (22)    Air (23)    Central axis of annular space (52)    Hole (54)