NOVELTY - The liquid fuel modification system has modifier (1), liquid fuel heater (9), unification unit (12), original fuel supply system (A), water vapor supply system (B) and reformed gas supply system. System (B) has water vapor generator (11) for supplying water vapor to system (A) and superheater (4) for superheating water vapor, such that temperature after mixing of liquid fuel and water vapor reaches beyond dew point of mixture.    USE - For modification of liquid fuel used for manufacture of hydrogen used in fuel cell electric power generation system.    ADVANTAGE - The liquid fuel modification system efficiently enables modification of liquid fuel, and ratio amount of energy of hydrogen consumed by fuel cell with respect to amount of energy of original fuel is high. The deposition of carbon is suppressed, and condensation of vaporized fuel and water vapor is prevented.    DETAILED DESCRIPTION - The liquid fuel modification system has a modifier (1), a liquid fuel heater (9), a unification unit (12), an original fuel supply system, a water vapor supply system and a reformed gas supply system. The modifier carries out modification reaction of fuel vapor obtained by vaporizing liquid fuel (101) with combustion heat of burner (1a), and water vapor (102a), and produces hydrogen rich reformed gas (110). The liquid fuel heater heats liquid fuel. The unification unit mixes heated liquid fuel and water vapor, and produces mixture (103) of fuel vapor and water vapor. The original fuel supply system has fuel preheater (2) for preheating mixture and supplying preheated mixture to modifier. The water vapor supply system has water vapor generator (11) for heating water (102), producing water vapor and supplying produced water vapor to original fuel supply system. The reformed gas supply system supplies reformed gas. The water vapor supply system utilizes heat of combustion exhaust gas (123) from reformed gas or burner. The water vapor supply system has water vapor superheater (4) for superheating water vapor, such that temperature after mixing of liquid fuel and water vapor reaches beyond dew point of mixture.    An INDEPENDENT CLAIM is included for liquid-fuel modification method.    DESCRIPTION OF DRAWING(S) - The figure shows the block diagram of liquid-fuel modification system. (Drawing includes non-English language text).    modifier (1)    burner (1a)    fuel preheater (2)    water vapor superheater (4)    liquid fuel heater (9)    water vapor generator (11)    unification unit (12)    liquid fuel (101)    water (102)    water vapor (102a)    mixture gas of fuel vapor and water vapor (103)    reformed gas (110)    combustion exhaust gas (123)