To provide a fastening plate which can surely fix a gypsum board to a subfloor gypsum board or the like in the installation or the overlapping of the gypsum board to a ceiling and a wall, is easy in handling, can reduce a work burden and shorten a construction time, and can suppress a construction cost.

This metal-made flat fastening plate is characterized in that there are arranged a pair of legs 4, 4 which are branched from a head 3, a crotch 9 is formed at roots of both the legs 4, 4, tip side ends of the legs 4, 4 are formed into folding fan shapes, and the legs 4, 4 are opened accompanied by the strike of the legs into the gypsum board.