Abstract: An opening/closing device for a discharge hole of a filter-drier is disclosed, in which an outer shell of a driving means for driving the opening/closing device of the discharge hole is sealed, so that during the discharge of the processed powders, the processed powders can be prevented from being introduced into the outer shell. A discharge tube 1 is fastened to the discharge hole 4 by means of a fastening device 1a, so that processed drug powders can be discharged though a discharge tube hole 4a. A cylindrical opening 2c is formed inside a flange 2b of the outer shell 2. A sealing cover 3b extends from the opening/closing plate 3 to be inserted into the opening 2c, and the sealing cover 3b is longer than the actuation distance of the opening/closing plate 3. The sealing cover 3b does not depart from the opening 2c, but is always maintained within the opening 2c to seal off the interior of the outer shell 2.