NOVELTY - A modifier (1) comprises catalyst unit (2) in oxidation region (4) which oxidizes by oxygen environment and is located in upstream of modifying region (3) which modifies hydrogen fuel and produces hydrogen, electric heater (5) which heats catalyst unit by supplying electricity to upstream of catalyst unit, catalyst temperature detection unit to detect temperature of each region of modifying region and oxidation region, air supply valve (7) which supplies air to catalyst unit via electric heater, and fuel injection apparatus (6) which supplies hydrogen fuel to catalyst unit via electric heater.    USE - A modifier for modifying hydrogen fuel and producing hydrogen (claimed).    ADVANTAGE - Damage to catalyst caused by water generated by oxidation reaction of mixed gas during start up of modifier can be avoided.    DETAILED DESCRIPTION - A modifier (1) comprises catalyst unit (2) in oxidation region (4) which oxidizes by oxygen environment and is located in upstream of modifying region (3) which modifies hydrogen fuel and produces hydrogen, electric heater (5) which heats catalyst unit by supplying electricity to upstream of catalyst unit, catalyst temperature detection unit to detect temperature of each region of modifying region and oxidation region, air supply valve (7) which supplies air to catalyst unit via electric heater, fuel injection apparatus (6) which supplies hydrogen fuel to catalyst unit via electric heater, and supply control unit which controls supply of hydrogen fuel and air with respect to catalyst unit based on temperature of modifying region and oxidation region detected by catalyst temperature detection unit. The modifier takes in hydrogen fuel and air which contains hydrogen as structural component from upstream channel, modifies hydrogen fuel, and generates hydrogen. At start of modifier, electric heater supplies electricity to catalyst unit and heats it. Supply control unit controls air supply valve and fuel injection apparatus to permit supply of hydrogen fuel or air with respect to catalyst unit until temperature of modifying region reaches 1st predetermined temperature which may bring about evaporation of water.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the modifier. (Drawing includes non-English language text).    Modifier (1)    Catalyst unit (2)    Modifying region (3)    Oxidation region (4)    Electric heater (5)    Fuel injection apparatus (6)    Air supply valve (7)