To provide a drying device, capable of performing continuous drying treatment of industrial waste containing water or the like.

The drying device comprises a furnace 10 including a burner 11 provided at an upper portion and a discharge port provided at a lower portion, and a plurality of cylinders (screw conveyors) 12 for carrying in, moving, and carrying out a workpiece to and from the furnace, a secondary combustion chamber 15 for heating exhaust air of the furnace, and a suction device 16 for sucking the exhaust air. The pressure in the furnace 10 is measured, and the suction device is controlled so that the inside of the furnace has a negative pressure to the atmospheric pressure. Since combustion gas is spread at the upper portion and fallen to the lower portion by disposing the burner at the upper portion, temperature unevenness depending on place within the furnace is minimized, and the whole furnace can be uniformly heated. Since the resident time within the furnace of the combustion gas can be controlled by controlling the suction quantity, the heat efficiency is improved. Further, the position of an upper conveyor which needs a large amount of calory gets close to the burner by disposing the burner at the upper portion, and the drying treatment time can be shortened.