PURPOSE: To enable discharge of powder object without pressurizing the interior of a tank by a method wherein a pair of screws for use in transfer of powder object flowing along a slide belt under a decreased pressure are oppositely arranged at the end of the belt to cause the powder of specific density to be discharged.

CONSTITUTION: Compressed air of decreased pressure required for transferring the powder with the slide belts 2, 2' arranged within a tank 1 is fed to the bottom part of the tank 1 through a compressor 13 and then the entire pressure in the tank 1 is discharged. A pair of screws 5, 5' oppositely faced to each other are arranged at the slant ends of the slide belts 2, 2' divided in halves by a wash plate 3 and the powder mixed with air is fed under a pressure to the oppositely arranged openings 5d, 5'd by means of screws 5, 5'. At the openings 5d, 5'd is disposed a spring 16 provided with valve means 18, 18' at both ends, the opposed openings 5d, 5'd are closed under a specific pressure. A density of the powder mixed with air is increased at this moment, the powder is discharged from the discharging port 9 and the powder is forcedly discharged through a discharging hose 15 from the air nozzle 19.