To provide a modified structure by efficiently improving the strength and appearance of an ALC external wall.

A connected bed material D formed by two members of a base bed material and an extension bed material is inserted into a through hole C, which is formed in the position where the bed material A of an existing ALC external wall B is arranged, and one of the ends of the connected bed material D is fixed to the existing bed material A, while the other end is protruded beyond the ALC external wall B surface and, after fixing a furring strip E arranged on the ALC external wall B surface, a new dry wall material F is fixed to the furring strip E. Thus not only execution can be carried out easily and fitting strength is ensured without disturbing residence but also the length of the connected bed material D itself can be adjusted, the difference of thickness of the ALC external wall B and regulating irregularity can be accommodated so an ALC external wall B modified structure of improved tensile appearance of the new dry wall material F and workability can be provided.