PURPOSE: To simplify joint work by forming both side end nail sections driven with U-shaped forked nails in a wide angle shape opened outward respectively and, at the same time, forming an intermediate joint section in the shape of a wide plate in a driving direction.

CONSTITUTION: Two through-holes 10 are bored in a wide plate-like joint section 2 and, at the same time, anchors 3 are welded vertically to both sides on the right end, and the anchor 3 is welded to the left end at a specific angle of inclination to form a large sized coupling metal fixture 1. After that, the coupling metal fixture 1 is such that the front ends of the anchors 3 are inserted into anchor insertion holes 5 of an upper girder 7 and that they are fixed with a hammer, etc. Then, a spliced girder 8 is mounted on the anchors 3 of the coupling metal fixture 1, and it is made to skid until an insertion cut 4 of the spliced girder 8 is fitted to a projected saddle provided to the plate-like joint section 2 to fit the anchors 3 to the anchor insertion holes 5. In addition, bolts 11 are inserted into the through-holes 10 to fasten both girders 7 and 8 and, at the same time, an U-shaped forked nail metal fixture 6 is driven across the insertion cut 4.