This sofa bed can be transformed into a fixed upper bed and into a lower bed with a sliding opening system. The second can be lifted by means of a suitable handle equipped with a patented safety system so as to avoid accidental closing. On the structure of the mechanism there are some holes for fixing the bayonets to make the fixing of the covered parts of the sofa simpler and quicker. It is realized with highly-resistant cold-rolled steel tube of top quality and it is lacquered with black epoxy resins in high temperature oven. It can be embedded after removing the armrests and the backrests. The several bed bases available are made up of slats and electro-welded mesh. It is designed for mattresses up to 15 cm. thickness. A simple and rapid assembly allows the sale of the kits.