PURPOSE: To obtain a device of a simple and practical structure superior in operability for reinforcing parts of a wall by reinforcing a rear side of a wall for supporting a large number of fixing elements such as screws, nails, dowels.

CONSTITUTION: A device for reinforcing a rear side of a wail 6 is provided with a bag 4 and a filling pipe 1. The bag 4 including a bridge 3 can be folded in the direction of insertion toward its center so as to be inserted through a drill hole 6a in the wall 6. The bag 4 in a returned position from folding is filled with hardenable mass 7 from the filling pipe 1, and a fixing element 5 is inserted between the radially surrounding ribs 2 of the filling pipe 1 for limiting the depth of insertion of the filling pipe 1. As the rear surface of the wall 6 is sufficiently reinforced when the hardenable mass 7 is hardened, it is possible to support fixing elements such as screws, nails stably.