To easily install a connecting reinforcement in a predetermined position in a connecting groove provided in a wall panel; and to prevent leakage of connecting grout.

The wall panel 1 has the connecting groove 2 formed on a lateral side; the connecting groove 2 for inserting the connecting reinforcement 3 is inclined downward from a surface of the panel 1; and the connecting reinforcement 3 is dropped into the connecting groove so as to be automatically housed on the bottom of the groove. Since the connecting reinforcement is automatically installed in a predetermined position, the operation of assembling the wall panel is simplified, and a construction period is shortened, so as to enable cost reduction. The connecting portion and connecting groove 2 of the wall panel 1 are covered with a connection assisting implement 6 to which sheet-like packing 61 is fixed, and filled with the grout. Thus, a job site can be kept clean without the leakage of the grout onto the surface of the wall panel; the operation of removing the leaked and consolidated grout becomes unnecessary; and connection and assembly can be efficiently performed.