(57) The bed assembly consists of a lifting apparatus set on tracks of a plane support where the patient can be positioned, such a support can be rapidly actuated by assembling three plane modular system where the first modular structure (1) operates as a modular stabilizing structure of a second counterposed couple of modular structure (2) which act as upright parts. To assemble the equipment, placed transversally on the floor under the bed the modular stabilizing structure (1) its corresponding clutching means (3) is to be inserted into the locking receptacles (4) of the upright modular structure (2) thus obtaining a U-shaped frame integrated structure fitted onto two couples of pivoting wheels (5) featured on the upright modular structures. In this way the lifting apparatus is placed in a condition interacting with the bed that, acting as a guideline between the end limits formed by the bedhead and foot of the bed, limits the apparatus movement to the only longitudinal translation so to place it either in a central position to suit bedside procedures when needed, or in a different position against the foot of the bed when no special treatment are needed. Inside the upper walls of the assembled upright modular structures (2), two couples of worm screw devices are provided for bearing and moving up and down two couples of holding hocks (6), going out from two counterposed vertical clefts (7), on which a plane lying support is to be set up by means of the application of its protruding eyelets (8). To carry out the up and down movement the shaft (9) is set in rotation, thus causing the vertical translation of the coaxial bodies (16) with inside threading engaged onto the guidelines (15) for the folding effect caused by clefts (7).