Abstract: A mobile-bottom device for swimming pools or hollow cavities comprising a frame (1) fixed to a meshed framework (2) comprising first profile sections (20) running in a first direction and belonging to at least one first plane P1 referred to as the upper plane, and second profile sections (21) superposed on the first profile sections (20) and running in a second direction preferably perpendicular to the first direction and belonging to a second plane P2 referred to as the lower plane and different from the first plane P1, means for raising and lowering the frame and the framework, means for motorizing the raising and lowering means.