To simply change a position for fixing a bath adapter by providing an opening or a cut-out at a specified position of a plate-like body being placed on a bathtub and a removable lid for covering the opening or the cut-out of the main body of the plate for installation.

The first opening 21 for connecting an adapter for an instrument for circulation of bathtub water is provided approximately at the central part of a plate-like body 20 being placed on a bathtub 3 and the second and the third openings 22 and 23 for connecting the adapter for the instrument for circulation of bathtub water being a little inclined are provided on the left and the right of the first opening 21 for connecting the adapter. In addition, a bath adapter 7 for the instrument for circulation of bathtub water is connected to one of the first, the second and the third openings 21, 22 and 23 for connecting the adapter for the instrument for circulation of bathtub water on its underside and a connecting joint 24 for connecting it to the functional part 4 of the instrument for circulation of bathtub water is fitted therein on its upper side and lids 25 are freely removably fitted in the remaining openings for connecting the adapter for the instrument for circulation of bathtub water. A fixing position for the bath adapter 7 can be simply changed thereby.