A joining device with minimum visibility for parts of furniture and furnishing items, in particular connecting a first panel to a second panel, which must be moved towards each other in an approach direction to bring the edge of one panel buffered in a tightening position against a surface of the other panel, includes a blocking group and a connection group assembled on the panels. The blocking group is inserted inside a seat contained in the thickness of the panel on which the blocking group is applied, and the seat has a longitudinal axis perpendicular to the approach direction, and extending from an edge towards the inside of the panels.