Abstract: Buffer storage unit for accumulating and releasing, in rows which are equidistant or have a programmed timing, products which arrive from a continuous advancement line and are arranged in non-equidistant rows, including a first conveyor belt (2) and a second conveyor belt (3) which are respectively actuated continuously and stepwise, and which have respective active portions (2a,3a) extending horizontally after one another. The belts are closed on themselves in a loop and are wound around respective sets of rollers, and the output roller (5a) of the first belt (2) and the input roller (7a) of the second belt (3) are mounted on a first slider (8) which is horizontally slidingly guided and which is associated with actuation elements which are controlled by sensors (16,17) which detect the presence of the products.