Belt-type vacuum packaging machine for packaging products (P) contained in preformed bags (B), comprising: - a base frame which supports a work surface which mainly develops along a longitudinal direction (X); - a conveyor belt which develops along said longitudinal direction (X) above said work surface and cooperates with advancement means to transfer products (P) contained in preformed bags (B) from a loading area to a packaging area ; - a packaging chamber arranged in said packaging area above said work surface and said conveyor belt ; - displacement means of said packaging chamber with respect to said work surface and said conveyor belt ; - a vacuum chamber configured to receive said products (P) contained in said bags (B) to be vacuum packed, said vacuum chamber being defined between the inside of said packaging chamber and an upper surface of said conveyor belt when a perimetric edge of said packaging chamber is arranged in contact with said work surface and said conveyor belt ; - at least one vacuum production system that communicates with said vacuum chamber ; - welding means of said preformed bags (B) adapted to be operated after vacuum packaging; - at least one injection system of at least one gaseous substance into each of said preformed bags (B) after said vacuum production system has created the vacuum in each of said preformed bags (B), said injection system comprising a plurality of injector nozzles that are configured to be connected to said preformed bags (B) and be turned towards the inside of said preformed bags (B) when said preformed bags (B) are arranged on said conveyor belt , characterized in that each of said injector nozzles belongs to said conveyor belt and is fixed in a through hole made in said conveyor belt . - a base frame which supports a work surface which mainly develops along a longitudinal direction (X); - a conveyor belt which develops along said longitudinal direction (X) above said work surface and cooperates with advancement means to transfer products (P) contained in preformed bags (B) from a loading area to a packaging area ; - a packaging chamber arranged in said packaging area above said work surface and said conveyor belt ; - displacement means of said packaging chamber with respect to said work surface and said conveyor belt ; - a vacuum chamber configured to receive said products (P) contained in said bags (B) to be vacuum packed, said vacuum chamber being defined between the inside of said packaging chamber and an upper surface of said conveyor belt when a perimetric edge of said packaging chamber is arranged in contact with said work surface and said conveyor belt ; - at least one vacuum production system that communicates with said vacuum chamber ; - welding means of said preformed bags (B) adapted to be operated after vacuum packaging; - at least one injection system of at least one gaseous substance into each of said preformed bags (B) after said vacuum production system has created the vacuum in each of said preformed bags (B), said injection system comprising a plurality of injector nozzles that are configured to be connected to said preformed bags (B) and be turned towards the inside of said preformed bags (B) when said preformed bags (B) are arranged on said conveyor belt , <EOS>