NOVELTY - A fuel treating apparatus (2) comprises modifier (4) for producing reformed gas which modifies source gas containing water vapor and hydrocarbon-type gas and contains hydrogen, burner combustor (5) which supplies heat to modifier, 1 or multiple carbon monoxide (CO) shift reaction device, wherein concentration of CO contained in reformed gas is reduced by CO shift reaction, gas flow path (22a) where waste gas discharged from burner combustor flows, water chamber (9b) which holds water between gas flow paths so that heat exchange is possible, and water evaporator (9).    USE - A fuel treating apparatus for fuel cell power generation system (claimed).    ADVANTAGE - Thermal efficiency of fuel treating apparatus is improved.    DETAILED DESCRIPTION - A fuel treating apparatus (2) comprises modifier (4) for producing reformed gas which modifies source gas containing water vapor and hydrocarbon-type gas and contains hydrogen, burner combustor (5) which supplies heat to modifier, 1 or multiple carbon monoxide (CO) shift reaction device, wherein concentration of CO contained in reformed gas is reduced by CO shift reaction, gas flow path (22a) where waste gas discharged from burner combustor flows, water chamber (9b) which holds water between gas flow paths so that heat exchange is possible, water evaporator (9) which allows heat exchange between waste gas which flows through gas flow path and water in water chamber and produces water vapor, water flow path which has water inlet and water outlet, gas outlet and gas inlet which have the same height, and water supply pre-heater (11) which pre-heats water introduced into water evaporator by waste gas. INDEPENDENT CLAIMS are included for:    (1) fuel cell power generation system which has fuel treating apparatus; and    (2) operating method of fuel cell power generation system.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the fuel cell power generation system. (Drawing includes non-English language text).    Fuel treating apparatus (2)    Modifier (4)    Burner combustor (5)    Water evaporator (9)    Water chamber (9b)