To subject the ground matter of used PET bottles to drying and crystallizing treatment at a low cost before the molding by a molding machine without deteriorating the physical properties thereof.

The apparatus for the drying and crystallizing treatment of the ground matter of the used PET bottles is equipped with a container 1 which is equipped with a ground matter inlet 2 for receiving the supply of the ground matter and a ground matter outlet 3 for discharging the ground matter after the drying and crystallizing treatment, the stirring means 4-15 for stirring the ground matter arranged in the container, the microwave radiation source 20 provided in the container to irradiate the ground matter in the container with microwaves and high pressure drying air feed-in means 21-24 for feeding high pressure drying air into the container from the bottom part thereof.