PURPOSE: To simplify the replacement of a panel by fitting a new panel to the panel locking pieces of a framework by means of a mortice and tenon method, after an existing panel has been removed from the framework.

CONSTITUTION: After a damaged existing panel G has been removed, male locking members 30 to 32 having male locking pieces 30a to 32a on three sides of the upper and lower frames 6, 7 and vertical frame 8 on the facing surfaces of an opened framework F are fixed by means of bolts 33. Then, that by which female locking members 34 to 36 have been fixed to the rear surface of a new panel G via a backup member 15 and a hardening type seal member 16 is prepared. Then, this new panel G is fitted to the upper and lower locking pieces 6a, 7a of the framework F by means of a mortice and tenon method, and the female locking members 34 to 36 are fitted to the male locking members 30 to 32 of the framework F. Thus, a damaged panel can be easily replaced by the operation only from the outside of a room.