An automatic loader of abrasive sand into a storage and supply tank (T) of a machine tool that uses the abrasive sand, and in particular of a cutting machine, includes a loading chamber (1) for loading the abrasive sand arranged above the supply opening of the tank (T) and having a suction inlet, connected through an air suction pipe (6) to a vacuum pump (2), and a sand inlet, in a lower position, connected through a sand suction pipe (7) to a supply container (S) for abrasive sand. A filter (F) is arranged inside the loading chamber (1), between the suction inlet and the sand inlet, and the loading chamber (1) is closed below by a butterfly valve (9) provided with spring element apt to retain the valve in the closed position when there is no sand inside the loading chamber (1).