To solve the problems that, when mounting a speaker on a curved ceiling panel of a bathroom unit, a baffle board is fixed to the lower side of the ceiling panel by fitting bolts, a packing is firmly pushed by the circumferential edge of the baffle board by the fixing by the fitting bolt to cause a crack in the baffle board and a crack in the packing by the circumferential edge of the baffle board and reduce the waterproof effect, and to provide the installation of a decorative cover protecting the packing by restricting the fastening degree of the packing, preventing deformation and breakage of the baffle board due to the crack by fastening by the fitting bolt, and preventing the enlargement of the external shape of a product.

A plurality of projections projecting rearward from the circumferential edge of the baffle board are provided, and when fastening the baffle board with the fitting bolts, the plurality of projections are served as substantially connecting parts between the ceiling panel and the baffle board while restricting a pushing pressure to an annular seal packing. Locking claws of the decorative cover are elastically locked to the inside of the annular flange in the circumferential edge of the baffle board.