PURPOSE: To contrive to improve evaporation capacity of evaporator, by making the base of evaporator in such a way that the base is in a slant of a falling gradient toward a flame direction.
CONSTITUTION: Plural reactors 3 are set at the upper part of an evaporator 1. A base 1a of the evaporator 1 is hollow in a dent state and the slant face of the base is made in a falling gradient toward a flame 2a of a burner 2. A liquid fuel sprayed from a fuel feed pipe 5 to the peripheral part in the evaporator 1 surely flows down toward the vicinity of the flame 2a and does not remain in a cold position. Consequently, evaporation capacity of the evaporator 1 is improved and the device can be miniaturized. Reactivity of steam modifying reaction in the reactors 3 can be improved.