PURPOSE: To promote unattended work which opens gradually the door of an entrance in order to cool gradually a burned article after burning.

CONSTITUTION: Male screwed members 17a and 17b, which are rotated by control motors 26a and 16b respectively, are mounted in a space 13 installed to the front in the lower part of both side walls of a furnace body 1 where screw bolts 18a and 18b are threaded thereinto respectively. A pair of pins 20 are arranged to stand on a support board 19 mounted at the tip of each screw bolt whereas a hinge 22 pivoted at the edges on both sides of a door 6 is fitted in between the paired pins 20 in such a fashion that it may be freely removed. After the burning is over, both screw bolts 18a and 18b advance intermittently according to the programs incorporated in control devices 27a and 27b, thereby pushing the door 6 so that it may be opened little by little up to an opening posture indicated by a chain line. In the means time, a burnt article in the furnace body 1 is gradually cooled.