Joining device, particularly for joining a shelf to a wall of a piece of furniture

A joining device, for joining a shelf to a wall of a piece of furniture, the joining device comprising:

• a cylindrical body that can be associated in a first hole adapted to be provided transversely in said shelf and provided with a first axial seat for the rotatable coupling of the first stem of a screw provided with a first crown-shaped head that can be arranged rotatably within a second seat adjacent to said first seat, wherein said cylindrical body is provided with a third seat, perpendicular and connected to said second seat, for the temporary coupling of a pinion, which interacts with said first crown-shaped head, which protrudes externally to said cylindrical body and is accommodated within a second hole adapted to be provided in said shelf, wherein said second stem of said pinion can be associated selectively and temporarily with said cylindrical body, said second stem being provided with an annular groove, which is provided proximate to its end, which interacts selectively with an annular ridge which protrudes proximate to the end of said third seat.