To contrive the improvement of the thermal expansion and contraction and weatherability of a building molding by interposing a cyanoacrylate based adhesive layer by the joining structure of a modified polyolefine based building molding and the other building molding.

Joining structure interposing an adhesive layer 3 is formed between one building molding 2 and the other building molding 2. In addition, the longitudinal sides 2a of the two building moldings 2, 2 are joined, one building molding part 2' is commonly joined on the surfaces 2b, 2b of the same side of the respective building moldings 2, 2, and the joining structure 1 interposing the adhesive layer 3 is formed on the joining face. Even the building molding having a surface containing modified polyolefine difficult to obtain sufficient adhesion force for a vinyl chloride solution adhesive can obtain the sufficient adhesion force by using cyanoacrylate as the adhesive. The molding is superior in thermal expansion and contraction and weatherability by making the laminate of a surface layer 42 containing a polyolefine based resin base body 41 and modified polyolefine.