A grinding device for denitrification catalysts comprises: a module that bundles a plurality of denitrification catalysts; a suctioning device that suctions air inside the denitrification catalysts through one end of the denitrification catalysts; a mixing device that disperses a grinding material for grinding the surfaces of the denitrification catalysts; a vertical duct that extends downward from the other end of the denitrification catalysts; a horizontal duct that extends from the mixing device in a direction intersecting with the direction of the vertical duct; and a relay device that redisperses the grinding material and that is a cylindrical member, the upper portion of which is connected with the vertical duct and a side face of which is connected with the horizontal duct.
