PURPOSE: To perform shredding work safely and efficiently by only performing reverse rotation of a rotary blade and opening of a guide plate and removing the charged abnormal material.

CONSTITUTION: A pair of rotary edges 3, 4 are provided in the lower step of the waste charging port 2 of a shredder main body 1. The rotary blade 4 of one side is provided in the lower position to constitute the rotary blade slanted in the direction of one side. Guide plates 5, 6 are provided in the upper step of the rotary blades. The guide plate 6 corresponding to the rotary blade 4 is separated into the upper part 7 and the lower part 8. A rotary shaft 10 is fitted to the top edge of the lower part. The lower part 8 is freely closed and opened downward while having the shaft as a supporting point. A motor 12 for opening and closing the lower part is fitted to the end of the shaft through a gearbox 11.