NOVELTY - A modifier comprises modifier (3) which carries out steam reforming of raw fuel gas, modifier burner (3a) which heats the modifier, modifier temperature measurement unit (3b) which measures temperature of the modifier, burner accommodating part which is in contact with modifier and accommodates the modifier burner, accidental-fire detection unit which detects accidental fire of modifier burner, ignition unit (3c) which lights the modifier burner, and ignition control unit (G) which makes the ignition unit implement the ignition retry operation.    USE - Modifier for fuel cell system.    ADVANTAGE - Thermal fatigue produced in modifier or burner accommodating part by the temperature change is prevented.    DETAILED DESCRIPTION - A modifier comprises modifier (3) which carries out steam reforming of raw fuel gas, modifier burner (3a) which heats the modifier, modifier temperature measurement unit (3b) which measures temperature of the modifier, burner accommodating part which is in contact with modifier and accommodates the modifier burner, accidental-fire detection unit which detects accidental fire of modifier burner, ignition unit (3c) which lights the modifier burner, and ignition control unit (G) which makes the ignition unit implement the ignition retry operation to which the re-start of the modifier burner is carried out when the accidental-fire detection unit detects accidental fire of modifier burner. The ignition control unit sets allowable frequency of the ignition retry operation by the relationship decreased as the temperature of the modifier measured by the modifier temperature measurement unit becomes high. The modifier which limits the frequency of ignition retry operation below the allowable frequency. An INDEPENDENT CLAIM is included for a control apparatus of modifier.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the fuel cell system to which the modifier is applied. (Drawing includes non-English language text).    Modifier (3)    Modifier burner (3a)    Modifier temperature measurement unit (3b)    Ignition unit (3c)    Ignition control unit (G)