PURPOSE: To improve efficiency in construction of an external wall by a method wherein an aluminum honeycomb core is provided between an outer peripheral frame and an inner peripheral frame, and an obverse and a reverse board, each having an opening, are attached and an opening for attachment of a panel body is made therewith.

CONSTITUTION: An exterior panel 2 is attached with fasteners to a space between an upper and a lower slabs comprising a building frame, and thereby an external wall is formed. Then, an opening 5 for attachment of a panel body is provided to the exterior panel 2 and a panel body 6 made of glass or the like is attached to the opening. An aluminum honeycomb core 12 is provided between an outer peripheral frame and an inner peripheral frame 11 of the exterior panel 2 and at the same time, an aluminum obverse board 13 and an aluminum reverse board 14 are stuck to the surface and the reverse side of the exterior panel, and a dent 45 of an exterior board 42 is made to be watertight with rubber 48. Therefore, the thickness in the direction toward the outside can be reduced, enlarging a space in the interior.