PURPOSE: To simply install a scaffold in a furnace.

CONSTITUTION: A beam for wire is inserted from the outside of an opening part 6 provided on one wall of a stopped furnace by means of a feed device, and the extreme end of the beam for wire is grasped from an opening part 7 provided on the other wall opposite to the opening 6. The wire 23 of a wire winding device 22 provided outside the opening part is connected to the extreme end of the beam for wire. Next, the beam for wire is returned to the initial position, so as to stretchedly install the wire 23 in the furnace. Next, a scaffold board 8 is fitted to the wire 23, drawn in the furnace by means of the wire winding device 22, and while supporting with supporting beams 5 already installed in the preceding stage, installed in the furnace, so as to build a long and slender scaffold. Next, safety cables 24 are stretchedly installed in the furnace by the similar method to the scaffold board 8, utilizing the beam for wire and the wire 23. Next, a required scaffold is constructed out of an accordion-like lengthy plate, utilizing the long and slender scaffold.