To enable supplying of fuel gas to be immediately stopped when an abnormal state such as cracking of an outer cylinder, prevent disasters such as fire and explosion or the like and further enable a safe operation to be carried out.

This heating device is constructed such that a ceramic cylindrical outer cylinder 16 having a bottom part is suspended into a molten tank 1 of molten metal 2, a combustion cylinder 20 for blowing out combustion gas toward the bottom part in the outer cylinder is suspended at the center of the outer cylinder 16, combustion gas discharged from the combustion cylinder 20 is reversed at the bottom part in the outer cylinder and discharged to an upper location in the outer cylinder 16. In this case, there are provided a gas supplying pipe 30 and an air supplying pipe 26 for supplying fuel gas and combustion air to the combustion cylinder 20. A pressure sensor 27 is arranged in the midway part of either the gas supplying pipe 30 or the air supplying pipe 26 and concurrently a shut-off valve 32 is arranged in the midway part of the gas supplying pipe 30 and then the shut-off valve 37 is shut off with an abnormal high pressure sensing signal of the pressure sensor 27.