To provide the joint forming structure of a sheet wall material by which an accurate joint of a specified width can be formed and at the same time, a technique for forming the joint of the sheet wall material by which any person can apply the sheet wall material easily and rapidly in an orderly state.

This joint forming structure is formed of a sheet wall material S laid all over an indoor side wall face or a ceiling face and each sheet wall material S has a thin joint piece 2 of a specified width on at least one of the edge sides of a decorative main body part 1. Further, these joint pieces 2 are applied in such a state that the pieces 2 are butted to the stepped parts of the edge sides of the decorative body part 1 in the adjacently facing sheet wall materials S. The technique for forming the joint of the sheet wall material S uses the described application means. In addition, the other means for the technique is to apply all over the surface the sheet wall material S having the thin joint piece 2 of a specified width on at least one of the edge sides of the decorative main body part 1, while being butted to the stepped parts of the edge sides of the decorative main part 1 in the adjacently facing sheet wall materials S, starting sequentially with the area where the materials S begin to be applied of the indoor side wall face or the ceiling face intended for the application.