PURPOSE: To stabilize blue flame combustion even if disturbance may occur during the combustion with a fixed amount by installing a curved surface installed at the inner surface of the cap-shaped hemisphere of a combustion cylinder and making easy the guide and reverse of emission direction of combustion gas.

CONSTITUTION: Air is supplied into the cylinder 5 of an atomizing nozzle part 2 by an air blower 8 and oil is atomized from an atomizing nozzle at a fixed angle by the fuel pump 24 of a controller 25 for the amount of oil and then ignited by an ignition electrode 7. When atomized oil is burnt, a combustion cylinder 12, a hollow cylinder 13, and a tapered vaporization cylinder 15 are heated by combustion heat. As the amount of oil is increased after a fixed time has elapsed, the atomized oil drops from the nozzle 6 are vaporized and combustion progresses from inside of each cylinder 12, 15 along the cylinder 13 to start blue flame combustion at a combustion part 16. As a ring-shaped closed wall 17 and the cylinder 12 are heated, normal combustion is effected even when the amount of oil is returned to that at the time of ignition and air is increased. Secondary air passing through an air hole 21 flows into an exhaust cylinder 9 for combustion gas to stop the overheat at each part of a burner and make combustion stabler.