An automatic screen changer device, especially suitable for being used on systems and equipment for the manufacturing, processing, recycling and treatment of thermoplastic materials, placed downstream of an extruder device and comprising: a frame on which stacked screening units (13, 13') are positioned, two opposite side plates or shoulders (14, 16) secured to said frame and provided, respectively, with an inlet opening and a pair of inlet channels, with an outlet opening and with a pair of outlet channels, wherein said inlet channels are suitable for allowing flowing and screening of contaminated molten material in the direction of the outlet channels through a pair of said stacked screening units (13, 13'), characterised in that said device comprises movable sealing and locking/unlocking means for a screening support or band for screening said molten material in each screening unit (13, 13') defined by a mobile wedge, longitudinally sliding inside of each of said screening units and provided with a through hole for the passage of the molten material coming from the inlet channel, wherein each of said screening units (13, 13') comprises a first plate, placed on the inlet side of the material, and a second plate placed on the outlet side of the material, said first plate and second plate being opposite and rigidly constrained one to the other, wherein said first plate and said second plate define an intermediate seat for accommodating said screening support or band, said intermediate seat being longitudinally developed along the whole length of said plates (22; 24) and suitable for receiving the screening support or band sliding inside said seat and supported by rollers rotatably driven by a motor, wherein said first plate and second plate are slidingly movable longitudinally with respect to the frame and to the opposite side plates or shoulders (14, 16) in a reciprocal way with temporary interruption of the flow of molten material through one of said same screening units during the screen change, wherein said first plate and said second plate comprise, respectively, a first chamber and a second chamber for the respective flow of molten material before and after screening, wherein said first plate comprises a pocket in which is accommodated said mobile wedge and wherein said through hole has a shape corresponding to that of the first chamber of the first plate. a frame on which stacked screening units (13, 13') are positioned, two opposite side plates or shoulders (14, 16) secured to said frame and provided, respectively, with an inlet opening and a pair of inlet channels, with an outlet opening and with a pair of outlet channels, wherein said inlet channels are suitable for allowing flowing and screening of contaminated molten material in the direction of the outlet channels through a pair of said stacked screening units (13, 13'), characterised in that said device comprises movable sealing and locking/unlocking means for a screening support or band for screening said molten material in each screening unit (13, 13') defined by a mobile wedge, longitudinally sliding inside of each of said screening units and provided with a through hole for the passage of the molten material coming from the inlet channel, wherein each of said screening units (13, 13') comprises a first plate, placed on the inlet side of the material, and a second plate placed on the outlet side of the material, said first plate and second plate being opposite and rigidly constrained one to the other, wherein said first plate and said second plate define an intermediate seat for accommodating said screening support or band, said intermediate seat being longitudinally developed along the whole length of said plates (22; 24) and suitable for receiving the screening support or band sliding inside said seat and supported by rollers rotatably driven by a motor, wherein said first plate and second plate are slidingly movable longitudinally with respect to the frame and to the opposite side plates or shoulders (14, 16) in a reciprocal way with temporary interruption of the flow of molten material through one of said same screening units during the screen change, wherein said first plate and said second plate comprise, respectively, a first chamber and a second chamber for the respective flow of molten material before and after screening, wherein said first plate comprises a pocket in which is accommodated said mobile wedge and wherein said through hole has a shape corresponding to that of the first chamber of the first plate.