PURPOSE: To easily move a slide plate to a position corresponding to the attaching position of a grip bar so as to correspond to a plurality of attaching positions using one reinforcing frame by slidably attaching the slide plate to the reinforcing frame located on the back side of a wall panel, and attaching the grip bar in position from the front side of the wall panel.

CONSTITUTION: Wall panels 2, 2 forming the side wall surfaces of a bathroom 1 are erected and corner frames 3, 3 are erected on the back side of the corner portions of the panels 2. A reinforcing frame 4 is horizontally suspended across the corner frames 3, 3 and held in position by screws or the like from the back side of the corner frames. Slide plates 5, 5 are slidably attached to the frame 4. The slide plates 5 are moved on-site relative to the reinforcing plate 4 as needed, stays 9, 9 are fitted into the panel holes 2a, 2a of the wall panel 2 from indoors, bolts 10, 10 are passed through the stays 9, 9 from indoors, and weld nuts are engaged with the bolts 10, 10 and fastened to hold the stays 9, 9 in position. A cap 11a rotatably provided to a grip bar 11 is engaged with each stay 9 from indoors to firmly attach the grip bar 11 in position on the wall panel 2.