PURPOSE: To prevent blow hole flames from forming to adjust to a smaller burning quantity so as to control an excessive flame in the case where the small burning quantity is adjusted to a large burning quantity by providing a flow straightening cylinder having a gap between inner and outer flame cylinders in the neighborhood of the position facing a wick inward of a furnace.

CONSTITUTION: A flow straightening cylinder 21 which is inward of a furnace 8 of an inner flame cylinder 6 and has a gap 21a with the inner flame cylinder 6 from upward of the lower end of the inner flame cylinder 6 in the neighborhood of the position facing a wick 1 is provided. With the constitution, passage resistance increases because air (arrow mark a) is supplied from air holes 11 through a narrow gap 21 and air is dispersed in the circumferential direction to be out of burning air fuel ratio. Accordingly, the exposure portion of the wick 1 and an inner fire dish 4 is protected from being heated without the formation of blow hole flames (f) in the air holes 11 in the neighborhood of or the faced portion of the wick 1 of the inner flame cylinder 6 even if the exposure height of the wick 1 is lowered to make a small burning quantity. In addition, an excessive flame because a gasified quantity can be reduced even if the small burning quantity is made a large burning quantity and the exposure of the wick 1 is heightened, and the production of CO, soot and an odor can be prevented.