Abstract: A device for compacting, on a first conveyor belt which is permeable to air, a solid substance consisting of loose particles, deposited in doses at regular intervals by dosing means which are synchronized with the first conveyor belt, comprises a second conveyor belt which moves at the same speed as and is located below the first belt, the second belt having through-holes at intervals along its length corresponding with the intervals used to deposit the doses of the substance; and vacuum means which are in continuous communication with the holes so that, through the first conveyor belt, they exert suction on the doses of the substance, keeping the particles of the substance together and in contact with the conveyor belt below them.