To obtain a heating furnace having a long service life of the core tube, less liable to cause the reaction of SiO2 with C even when using at the time of drawing an optical fiber and capable of enhancing the strength of the optical fiber by forming a coating layer of at least one among TiC, ZrC and HfC on at least the inner surface of a carbon-base core tube.

The heating furnace has a carbon-base core tube housing a body to be heated and a coating layer of at least one among TiC, ZrC and HfC has been formed on at least the inner surface of the core tube or at least the inner surface of the core tube is made of at least one among TiC, ZrC and HfC. The carbon is preferably high purity graphitic carbon having ≤10 ppm ash content and amorphous carbon is especially preferably used. It is also preferable that amorphous carbon is used as a middle layer between the high purity carbon-base core tube and the carbide coating layer.