An 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 comprising to close said displaceable part: - a mobile first cursor guided such as to be selectively engageable with drawing pins (39, 40, 43) operatively connected to the displaceable part of the article of furniture, said drawing pins comprising a front drawing pin, a rear drawing pin and an intermediate drawing pin, both being shorter than the front drawing pin, the first cursor further having a recess engageable by the front drawing pin in the closed position in normal use; - a guide in which the first cursor is slidable, said guide having a longitudinal guide tract, a first transversal guide extending at one end of said longitudinal guide tract and second and third transversal guides extending at the other end of said longitudinal guide tract, said first cursor having a special tab engageable by intermediate drawing pin which frees the first cursor from the second and third transversal guides during opening, during closing the rear and intermediate drawing pins (40, 39) pass beyond the recess while the longer front drawing pin engages the recess; - first elastic elements, operatively connected to said first cursor, said first elastic elements soliciting the first cursor in a closing direction of the displaceable part of the article of furniture and holding said first cursor in the closed position in normal use; - a linear decelerator provided with a stem adapted to intercept a stop provided on a displaceable guide part applicable to the displaceable part of the article of furniture; the automatic opening and closing device comprising to open said displaceable part: - a n ejector comprising second elastic means for soliciting the article of furniture in the opening direction, said second elastic means having less rigidity than the first elastic elements; characterised in that said retaining device comprises: - a second cursor, mobile along a first sliding guide on a base body such as to be selectively engageable with said drawing pins (39, 40, 43); - a hooking element connected movably to the second cursor and selectively slidable along a second sliding guide or along a third sliding guide provided in said base body; and - blocking means in said base body, associated to said third sliding guide for releasably blocking said hooking element against the force of said second elastic means, when the article of furniture is in the closed position after having been partially opened. - a mobile first cursor guided such as to be selectively engageable with drawing pins (39, 40, 43) operatively connected to the displaceable part of the article of furniture, said drawing pins comprising a front drawing pin, a rear drawing pin and an intermediate drawing pin, both being shorter than the front drawing pin, the first cursor further having a recess engageable by the front drawing pin in the closed position in normal use; - a guide in which the first cursor is slidable, said guide having a longitudinal guide tract, a first transversal guide extending at one end of said longitudinal guide tract and second and third transversal guides extending at the other end of said longitudinal guide tract, said first cursor having a special tab engageable by intermediate drawing pin which frees the first cursor from the second and third transversal guides during opening, during closing the rear and intermediate drawing pins (40, 39) pass beyond the recess while the longer front drawing pin engages the recess; - first elastic elements, operatively connected to said first cursor, said first elastic elements soliciting the first cursor in a closing direction of the displaceable part of the article of furniture and holding said first cursor in the closed position in normal use; - a linear decelerator provided with a stem adapted to intercept a stop provided on a displaceable guide part applicable to the displaceable part of the article of furniture; - a n ejector comprising second elastic means for soliciting the article of furniture in the opening direction, said second elastic means having less rigidity than the first elastic elements; - a second cursor, mobile along a first sliding guide on a base body such as to be selectively engageable with said drawing pins (39, 40, 43); - a hooking element connected movably to the second cursor and selectively slidable along a second sliding guide or along a third sliding guide provided in said base body; and - blocking means in said base body, associated to said third sliding guide for releasably blocking said hooking element against the force of said second elastic means, when the article of furniture is in the closed position after having been partially opened.