A brine filtering device, applicable to a meat product injection machine, comprising a pre-filtering unit having: a first pre-filtration drum and a second pre-filtration drum arranged to rotate coaxially together about a horizontal rotation axis and respectively provided with a first filtering wall and a second filtering wall around said horizontal rotation axis; an inlet hopper configured to receive brine to be filtered and to force it into said first pre-filtration drum through said first filtering wall at an upper region thereof; a tub arranged to collect the brine filtered through the first filtering wall which exits the first pre-filtration drum at a lower region thereof, wherein the second pre-filtration drum is partially submerged in the brine contained in said tub, the brine from the tub enters into said second pre-filtration drum through said second filtering wall in a lower region thereof, and the brine is poured from the second pre-filtration drum into a tank through an open side wall of the second pre-filtration drum; a first scraper arranged to scrape the outer surface of the first filtering wall of the first pre-filtration drum and a first ramp arranged to direct the waste pulled off by said first scraper to a collection tray; and a second scraper arranged to scrape the outer surface of the second filtering wall of the second pre-filtration drum and a second ramp arranged to direct the waste pulled off by said second scraper to a collection tray; and a safety filtering unit having: at least one safety filter sleeve submerged in said tank into which the brine is poured from the second pre-filtration drum, said safety filter sleeve being connected to an outlet of said tank; and suction means for sucking the brine contained in the tank through said safety filter sleeve and through said outlet, characterized in that: a retaining member is arranged to skim the outer surface of the first filtering wall of the first pre-filtration drum at an upper region thereof; and a driving mechanism is arranged to intermittently move said retaining member out of contact with the first filtering wall to let the first pre-filtration drum move waste accumulated by the retaining member to said first scraper. a first pre-filtration drum and a second pre-filtration drum arranged to rotate coaxially together about a horizontal rotation axis and respectively provided with a first filtering wall and a second filtering wall around said horizontal rotation axis; an inlet hopper configured to receive brine to be filtered and to force it into said first pre-filtration drum through said first filtering wall at an upper region thereof; a tub arranged to collect the brine filtered through the first filtering wall which exits the first pre-filtration drum at a lower region thereof, wherein the second pre-filtration drum is partially submerged in the brine contained in said tub, the brine from the tub enters into said second pre-filtration drum through said second filtering wall in a lower region thereof, and the brine is poured from the second pre-filtration drum into a tank through an open side wall of the second pre-filtration drum; a first scraper arranged to scrape the outer surface of the first filtering wall of the first pre-filtration drum and a first ramp arranged to direct the waste pulled off by said first scraper to a collection tray; and a second scraper arranged to scrape the outer surface of the second filtering wall of the second pre-filtration drum and a second ramp arranged to direct the waste pulled off by said second scraper to a collection tray; and a safety filtering unit having: at least one safety filter sleeve submerged in said tank into which the brine is poured from the second pre-filtration drum, said safety filter sleeve being connected to an outlet of said tank; and suction means for sucking the brine contained in the tank through said safety filter sleeve and through said outlet, characterized in that: a retaining member is arranged to skim the outer surface of the first filtering wall of the first pre-filtration drum at an upper region thereof; and a driving mechanism is arranged to intermittently move said retaining member out of contact with the first filtering wall to let the first pre-filtration drum move waste accumulated by the retaining member to said first scraper. at least one safety filter sleeve submerged in said tank into which the brine is poured from the second pre-filtration drum, said safety filter sleeve being connected to an outlet of said tank; and suction means for sucking the brine contained in the tank through said safety filter sleeve and through said outlet, characterized in that: a retaining member is arranged to skim the outer surface of the first filtering wall of the first pre-filtration drum at an upper region thereof; and a driving mechanism is arranged to intermittently move said retaining member out of contact with the first filtering wall to let the first pre-filtration drum move waste accumulated by the retaining member to said first scraper. a retaining member is arranged to skim the outer surface of the first filtering wall of the first pre-filtration drum at an upper region thereof; and a driving mechanism is arranged to intermittently move said retaining member out of contact with the first filtering wall to let the first pre-filtration drum move waste accumulated by the retaining member to said first scraper.