Embeddable mechanism provided with front opening system through one simple rotation of the backrest. The sofa is converted into sofa bed without removing the covers. The system is fitted with a bayonet supporting steel frame that allows to fasten the armrests and the backrest to the system. It is therefore possible to fasten several models of armrests and backrests. The bed base is made up of a rectangular electrowelded wire mesh to make the sofa more resistant, stronger and durable. The backrest is equipped with one storage compartment for pillows. The bed base is provided with a 17 cm. spring mattress.