The assembly of an automatic opening and closing device and a retaining device for a displaceable part of an article of furniture. The automatic opening and closing device includes a first cursor (8) mobile such as to be selectively engageable with drawing pins (39, 40, 43) operatively connected to the displaceable part of the article of furniture; a first elastic elements (9), and a second elastic element. The retaining device includes a second cursor (21), mobile along a first sliding guide (20) on a base body (19) such as to be selectively engageable with the drawing pins; a hooking element (23) connected movably to the second cursor (21) and selectively slidable along a second sliding guide (22) or along a third sliding guide (24) provided in the base body (19), and blocking elements in the base body (19), associated to the third sliding guide (24) for releasably blocking the hooking element (23).