To provide a heat treatment furnace that uses, as a main heat insulator, a press compression-molded article of ceramic fine particles which are brittle and have large heat shrinkability, but have superior heat insulating properties.

There is provided a heat treatment furnace that has a floor portion and both sidewall portions which are constituted by stacking a heat-shrinkable heat insulator and a heat-expandable heat insulator formed of press compression molded articles of ceramic fine particles by alternately stacking, and also has a ceiling portion formed by alternately stacking heat insulators similar to the above heat insulators on both the sidewall upper portions. Preferably, each heat-expandable heat insulator has a larger coefficient of thermal expansion in a thickness direction than a coefficient of thermal expansion in a horizontal direction. More preferably, a sum of absolute values of coefficients of thermal expansion of the heat-expandable heat insulators and heat-shrinkable heat insulators in the horizontal direction is 5% or less.