To obtain a support device which reduces labors and a construction period and cost by constituting a support part installed in a double-board support member so as to support the forward and rearward boards at the rear side part and providing the support part at the forward and rearward sides of the body.

Boards 2, 3 parallelly arranged forward and rearward are supported by a support member 1 and a forward support part 5 and a rearward support part 6 are provided in a hollow body 7. The forward and reaward support parts 5, 6 support the boards 2, 3 at the rear side parts 9, 10, and inclined projections 31 are formed at the tips 28 of turned-back plate parts. The right and left symmetrical half-split bodies 11, 11 are integrally formed back to back in the support member 1. The ends 39 of the forward board 2 are fixed on the support parts 5 and the ends 42 of the rearward board 3 are fixed on the support parts 6 with screws 41 respectively. In this way, the forward and rearward boards 2, 3 can be supported from the same side of the support member 1 and hence, a high quality execution can be efficiently carried out in a short period. Further, thickness of a wall can be reduced and decrease of a room space can be suppressed minimally.