PURPOSE: To dry and crystallize a powdery or granular material in a short time by radiating microwaves to the powery or granular material in a drying tank provided with a material inlet and an outlet, floating the powdery or granular material being heated, introducing dehumidified air into the floating powdery or granular material in the treating tank and exhausting moist air passed through the powdery or granular material.

CONSTITUTION: A powdery or granular material composed of a synthetic resin material is fed from a material inlet 11 into a treating tank 1 and heated up by microwaves. The powdery or granular material introduced in is floated on a floor 6 by the vibration of the treating tank 1 in the arrow direction generated by a floating device to remain successively in a residual section 18. At that time, spaces in a layer formed by the powdery or granular material are enlarged by floatation, and the material can be in contact with dehumidified air introduced from a blowing tube 41 efficiently, while the contact of respective powdery or granular materials is lessened, and the dehumidified air introduced from the blowing tube 41 absorbs efficiently the water content from the powdery or granular material heated from inside by the microwaves to turn into moist air and is exhausted out of the treating tank 1.