To solve such problems that, conventionally, a flaking machine for PET bottles (made of polyethylene telephthalate) is a heavy and large-sized machine and much cost and time are required for polishing, adjustment and maintenance of shredding blades of the machine and thereby the recycled material price is increased and becomes a bottleneck in material recycling, and accordingly, resource conservation and environmental conservation are adversely affected and piling-up of accumulated PET flakes is caused.

This shredder 10 of a PET bottle flaking machine is provided with a backward flow prevention plate 9 for preventing any backward flow of PET bottles being conveyed under pressure, from being caused during the shredding of them, to enable securance of safety and increase of shredding capacity of the machine, and also formed as a cartridge, so as to be safely replaceable by another one in a short period of time, to eliminate unnecessary shutdown time of the machine and to reduce the size of the machine to a possible minimum. Further, the PET bottle flaking machine has a blower 19 inside, in order to realize high efficiency of the machine.