To prevent the head sections of bolts from being exposed on a decorative surface by fitting a presser metal having a bent cross section to be kept in contact with the step section of a second plate bonded to the back face of a first plate to the second plate with push bolts screwed to rasp-cut nuts at the peripheral edge section through the presser metal.

The peripheral edge of a second plate 23 is located on the inside of the peripheral edge of a first plate 22 to form a staircase-like step section, and many rasp-cut nuts 28a, 28b are buried at the peripheral edge section of the second plate 23 while a flange section 33 is faced to the inside. When a background panel 21 is to be fitted to a casing, push bolts 30 are screwed to the rasp-cut nuts 28c via through holes to fix the upper end section of the background panel 21, and a push bolts 39 are screwed to the rasp-cut nuts 28a through a fitting plate 10 to fix the lower end side of the background panel 21 to a stanchion. The push bolts 39 are screwed to the rasp-cut nuts 28b to fasten the fitting section 47 of a title box via a presser metal 34.