To enable a heat treatment to be carried out at a higher temperature than that attained where eutectic mixture material is formed between heat treated material and a floor material by a method wherein a contacting position between a bottom part and a furnace chamber lining material is arranged at a position where a temperature in which molten phase is formed between materials contacted to each other at the contacting position during a heat treatment process.

A segment 20 at a bottom surface 19 of a furnace chamber where heat treated material is placed is constituted by the material having the same chemical composition as that of the heat treated material or similar to that of the heat treated material. In addition, the bottom segment 20 is arranged such that it may not be contacted physically with other linings in a furnace chamber 15. In addition, the bottom segment 20 of a furnace structure is arranged at such a position where a contact position 21 between the bottom segment 20 and a furnace chamber lining material 10 having the bottom segment arranged thereat during a heat treatment process shows a temperature lower than a temperature in which molten phase is formed between the materials to be contacted to each other at the contacting position.