PURPOSE: To eliminate an excessively high temperature region, to prevent a creeping deformation, etc., due to deformation by thermal stress of the inner face of a heat insulating layer, its own weight, and to largely improve a lifetime by disposing temperature measuring means of a lowermost part at a position becoming substantially the same temperature as that of the vicinity of the upper face of an article-to-be-treated placing base in a temperature holding state.

CONSTITUTION: Temperature measuring means 22 of at least at a lowermost part (only at the lowermost part in this embodiment) of a plurality of temperature measuring means 19 - 22 is disposed outside a heater supporting cylinder 13, and the remaining temperature measuring means 19, 20, 21 are disposed inside the heater supporting cylinder 13. The temperature measuring position of the temperature measuring means 22 is set to a position substantially the same as that of the temperature in the vicinity 23 of the upper face of an article-to-be- treated placing base 8. According to this constitution, an excessively high temperature region is completely eliminated to prevent creeping deformation, etc. due to deformation of thermal stress of the inner face of the heaters 9 - 12, the heater supporting cylinder 13, the heat insulating layer 7, its own weight, to largely improve lifetime and to improve soaking properties of a treating chamber 6 in a temperature holding state.