PURPOSE: To attain mutual tight connection by setting the projecting length from an end surface of a connecting element fixed to a first structural angle larger than a certain specific distance toward the second structural angle side to end surfaces where a welding part with the second structural angle allows the mutual structural angles to tightly abut to each other.

CONSTITUTION: A connecting element 20 is immovably fixed to a web 12 arranged in a hollow space 4 of a first structural angle 2 so as to project from an end surface of the structural angle 2, and this connecting element 20 is connected to a web 13 in a hollow space 5 of a second structural angle 3 via a welding part 32. The length 24 of the connecting element 20 projecting in the hollow space 5 of the structural angle 3 is set larger than a certain specific distance toward the structural angle 3 side to end surfaces 22, 23 where the welding part 32 allows the structural angles 2, 3 to tightly abut to each other. Thus, the mutual structural angles 2, 3 can be tightly connected by the approach after the structural angles 2, 3 cut off a welding current and the approach by cooling of the welding part 32.