To avoid the property dispersion of a heated object by suppressing the escape of heat from a heat treatment space through supporting columns to the outside to suppress the temperature dispersion of the heated object.

This heat treatment furnace comprises a furnace body 10 having a heat treatment space inside, a hearth 14 formed of a light heat insulating material and arranged on the bottom of the furnace body 10, a plurality of supporting columns 17 each having a lower end terminated inside the hearth 14 and an upper end exposed to the upper face of the hearth 14, a bed plate 18 on which the heated object W arranged on the supporting columns is placed, and a supporting material 19 arranged inside the hearth 14 for supporting the plurality of supporting columns 17 at their lower ends and having strength greater than the light heat insulating material. The supporting columns 17 are constructed to be stopped inside without passing through the bottom face of the hearth 14, thus suppressing the radiation of heat. The supporting material 19 supports the supporting columns 17 at their lower faces to prevent the sink-down of the supporting columns 17.