PURPOSE: To reduce the number of operations by a method in which a flat plate having rivet holes and wire holes is bent into an angled form, and two pieces of the angled plates are combined into a pipe form and joined to each other.

CONSTITUTION: Column parts 20 are set on given positions in such a way as to enable panels 10 to connect to lipped angled parts 21 to make up the column part 20. The panels 10 are placed to turn the flat panel 11 outside of room between the column parts 20 to connect the panels 10 with the column parts 20 by rivets. After all the panels 10 are attached, an electric wire 3 is passed through the parts 10 and 20 and a copper foil tape 31 is applied to the joint of the panels 10 and wall panels 35 are attached to the indoor side. Holes 22 and 23 necessary for the column parts 20 can thus be exactly formed in the flat panel 11 before forming the column parts 20 by using a turret punch or others by reducing the number of the holing operations.