PURPOSE: To enhance the operating easiness by allowing the upper ridge oversurface of a mounting member to bear the upper ridge undersurface of a tile block, and holding the projection end of a support piece of a holder metal detained with a lower groove resiliently at the lower ridge undersurface of the mounting member.

CONSTITUTION: At a mounting member 1 an upper and a lower ridge 1b, 1c protrudes parallelly, and an upper, a middle and a lower ridge 21, 22, 23 protrude at the rear side of a tile block 2, and further an upper groove 24 and a lower groove 25 are formed. A detaining fixture 31 for a holder metal 3 formed from a resilient metal plate is provided accommodatable in this groove 25. The mounting member 1 is fixed to the mass body, and the mounting part 31 is detained with the groove 25 in the block 2. The block 2 in this condition is held fast at the upper and lower ridges 1b, 1c of the mounting member 1, and the projection end of a support piece 32 is held resiliently at the ridge 1c. This should enhance the operating easiness.