Constituent device for furniture which comprises a base, a strut, an elastic means and a fixing means such that the base and the strut are joined to each other and in a notably perpendicular mutual position and the elastic means is in a position interposed in the joining region between the base and the strut and said elastic means being fixedly connected on the strut and also connected in a movable position close to the joining between the base and the strut, in which said elastic means is enabled and in a suitable position for the interposition between the same and the base of a notably flat exterior body, and the fixing means has the capacity to fix to said elastic means in an immovable and rigid position with the notably flat exterior body embedded and tightened between the elastic means and the base.