PURPOSE: To prevent toxic gas from being generated when a combustion power is adjusted by a method wherein a resistive plate is arranged within a dome-like flame holding fitting installed to cover an upper part of one end of a divided wick in such a way that the resistive plate is positioned inside the end part of the divided wick at the combustion side.

CONSTITUTION: When one of divided wicks 11 is lowered to extinguish flame in order to adjust a combustion power, an upper part of a divided wick 11 is covered by a shielding plate 18 at a flame extinguishing part and then a temperature of the flame is decreased. At this time, air flowing from the flame extinguishing side into the combustion side through the flame holding fitting 16 is adjusted for its flow rate by a resistive plate 17 and a pilot flame within the flame holding fitting 16 is superiorly held. A combustion cylinder is vibrated in order to make a uniform flame to be held in aeration holes when the combustion power is changed over from a weak combustion power to a high combustion power, and further in case that the flame holding fitting 16 is moved within a moving range of a sitting operation for the combustion cylinder with its resitting operation, the resistive plate 17 is not removed from the divided wick 11 at the combustion side, a flow passage resistance within the flame holding fitting 16 is not varied, a flow rate of air flowing into the combustion side is always kept constant, and the pilot flame within the flame holding fitting 16 is held in a good condition.