Anti-flooding safety device for a washing machine, in particular for household use, said device comprising a valve body in which a duct is defined for the passage of a liquid, comprising: - an inlet section, for connecting the device to a liquid supply source; - an outlet section for connecting the device to a supply tube for supplying said liquid into a washing machine, wherein a second tube surrounds the supply tube, thereby forming a hollow space; - an intermediate section having a passage for the liquid and connecting said inlet section to said outlet section, wherein the anti-flooding device comprises: - a shut-off device comprising a closing element movably arranged in said intermediate section for opening and/or closing said passage, said closing element comprising a first magnet; - an actuation device positioned, at least partially, in a chamber of the valve body in fluidic communication with the hollow space, said actuation device comprising a second magnet mounted on a rotary holder, wherein the holder is associated with a blocking element arranged to retain the holder and the second magnet in a first position, so as to repel the first magnet with opposite polarization and preload the shut-off device by means of the first magnet in order to keep the passage open; - a reaction element, which reacts with the leakage liquid entering the chamber of the valve body through the hollow space, said device being characterized in that: said reaction element consists of a flexible membrane associated with the blocking element, said flexible membrane being sensitive to the increased pressure in the chamber caused by a leakage from the first tube and being adapted to produce a displacement of the blocking element, wherein said displacement frees the holder, which will then turn also because of the repulsion between the first magnet and the second magnet, and move the second magnet from said first position to a second position, in which the second magnet exerts attraction on the first magnet in order to close the passage. - an inlet section, for connecting the device to a liquid supply source; - an outlet section for connecting the device to a supply tube for supplying said liquid into a washing machine, wherein a second tube surrounds the supply tube, thereby forming a hollow space; - an intermediate section having a passage for the liquid and connecting said inlet section to said outlet section, - a shut-off device comprising a closing element movably arranged in said intermediate section for opening and/or closing said passage, said closing element comprising a first magnet; - an actuation device positioned, at least partially, in a chamber of the valve body in fluidic communication with the hollow space, said actuation device comprising a second magnet mounted on a rotary holder, wherein the holder is associated with a blocking element arranged to retain the holder and the second magnet in a first position, so as to repel the first magnet with opposite polarization and preload the shut-off device by means of the first magnet in order to keep the passage open; - a reaction element, which reacts with the leakage liquid entering the chamber of the valve body through the hollow space,