walls a ceiling and a floor each divided into a plurality of sections a heater block mounted on each section a thermal sensor mounted to each heater block and a thermal controller to control heating of the heater blocks based on a temperature measured by the thermal sensor application_number US 30550502 A description fig1 a is a partially cut out perspective view of a heat treatment furnace of a soaking apparatus according to the present invention fig1 b is a perspective view illustrating a wall structure of the furnace of fig1 a and fig2 is a partially cut out perspective view showing sections formed on walls a ceiling and a floor of the furnace of fig1 a a heat treatment furnace 14 of a soaking apparatus 1 of this embodiment is a batch type furnace and has a ceiling 2 a floor 3 a front wall 4 a rear wall 5 a left wall 6 and a right wall 7 each inner surface of the ceiling 2 the floor 3 and the walls 4 to 7 is divided into three sections as shown in fig2 the heart heat treatment furnace 14 is provided with heater blocks a b and c on a surface of the floor 3 heater blocks d e and f on a surface of the ceiling 2 heater blocks g h and i on a surface of the front wall 4 heater blocks j k and l on a surface of the rear wall 5 heater blocks m n and o on a surface of the right wall 7 and the heater blocks p q and r on a surface of the left wall 6 referring to one of the walls.