PURPOSE: To prevent an excessive large flame when the combustion rate is changed from low to high by providing an air supply device that supplies air into a combustion chamber linking with a wick adjusting device, and a controller that reduce the capacity of the air supply device gradually and stops it after a certain period of time when the combustion rate is changed from low to high.

CONSTITUTION: A cylindrical wick 1 that is installed vertically is held free to move up and down between a wick internal drum 4 and a wick external drum 5, and the lower end of the wick 1 is submerged into liquid fuel. The exposed height of the top of the wick 1 in a combustion chamber 11 is adjusted by a wick adjusting device 14 to regulate the combustion rate. A blower 15 as an air supply device is installed in the wick internal drum 4 so as to produce an air current flowing from the top toward the bottom. A controller 16 that regulates the output of the air fan is linked with a wick adjusting device 14. In this constitution described above, when the combustion rate is rapidly changed from weak to strong, the blower 15 is started to supply air into an internal combustion drum 3, and the combustion load is increased, so that generation of a excessive flame can be prevented. However, when the blower 15 is stopped, the flame grows rapidly. This phenomenon can be solved by providing the controller 16 that reduces the output of the blower 15 gradually and stops it after a certain period of time.