PURPOSE: To install a wall board on a wall surface easily and quickly by attaching both the end portions of the wall board to the sash bar of the wall surface with attaching fittings and the main body of an attaching device respectively and also fitting a bottom joint to a recessed portion of an end portion of adjacent wall boards.

CONSTITUTION: Fittings 8 is attached to a sash bar 7 by fixing an attaching piece portion 10 of attaching fittings 8 to the sash bar 7 of a wall surface 1 with a fixing device 23. Next, one fitting portion 21 of the main body 9 of an attaching device is fitted to one recessed groove 6 of a wall board 2, other recessed gutter 5 is linked to a linking piece 12 of the fittings 8, and an attaching piece portion 30 of the main body 9 is fixed to the sash bar 7 with the fixing device 23, and the main body 9 is attached to the sash bar 7. Next, the side end portion 25a of one of the bottom joint 24 is fitted to a recessed groove 6. Then, other side end portion 25b of the bottom joint 24 is fitted to a recessed groove 5 of other wall board 2 with the main body 9 attached to the outer projected portion 20 of the recessed groove 6. In addition, the outer projected portion 20 of other recessed groove 5 of the other wall board 2 is fitted to other fitting portion 21 of the main body 9 attached to the sash bar 7.