To position right and left angle members correctly by connecting a pair of right and left metal angle members whose corner portions are linked by engaging hardware by a plate member in a direction perpendicular thereto.

To couple both beam members 11, 12, first of all, a groove 13 provided in the beam member 11 and a convex portion 14 provided in the beam member 12 are fitted to each other. And then the groove 13 and the convex portion 14 are reinforced through fitting hardware 15 so that excessive stress may not work on them intensively. The fitting hardware 15 is attached by fitting the angle members 16, 16 coupled with a plate member 17 into the corner C of the beam members 11, 12 and driving nails into nail holes 18. And then, a strap connecting device 20 is inserted into a through hole 19 and bolted to the beam member 12 using a bolt hole provided in the strap 22, and a nut is hung on a threaded rod provided in the shaft portion and tightened. Therefore, the fitting hardware is easy to handle, and the reinforcing function by which the relative positions of the right and left angle members to be arranged on both sides of the beam members are retained, are improved further.