To secure sufficient joining strength for a joint between a pipe body and a part to be connected, which are joined together by a noncircular fastening metallic material, in a joining structure for the pipe body or for a building unit by means of the fastening metallic material.

The joining structure for the pipe body 12 is constitutionally provided with an end plate 20, which is installed at the end of the pipe body 12 and has a noncircular insertion hole 21 and a fastening surface 22 fitted with a sloping surface along a peripheral direction, and the fastening metallic material 30 screwed into the part to be connected, formed in a noncircular shape enabling insertion into the insertion hole 21 of the end plate 20 and fastened to the fastening surface 22 of the end plate 20.