To positively prevent a joint cut-off member from being damaged and slipping out, by using a compressed joint cut-off member formed of a shape- memory resin, attaching the member to an external wall panel before erection, and restoring and expanding the member by heating after the erection.

A compressed cut-off member 2 is arranged and installed in a depression 1a of an external wall panel 1 in the factory or in the construction field. The installation of the member 2 may be carried out by using an adherent or the like. Then, erection of the external wall panel 1 is carried out in the construction field. The cut-off member 2 has been compressed, and therefore it is not damaged nor slipped out due to rubbing of both the adjacent external wall panels 1, 1. After the erection, hot blast is blown to a gap between the external wall panels 1, 1 by means of a drier 3 or the like, to thereby heat the compressed cut-off members 2 at a glass transition temperature or more. Thus, the cut-off member 2 is restored and expanded, and assumes a state of suitably placed in a joint, which leads to a cut-off state at a joint between the external wall, panels 1, 1.