PURPOSE: To uniformly and rapidly dry a large quantity of plastic pellets, by mounting several small capacity drying chambers each equipped with a magnetron to one large capacity hopper and successively charging the plastic pellets dried by the small capacity drying chambers to the large capacity hopper.

CONSTITUTION: Eight drying chambers 11 are provided to the upper part of a hopper 10. Plastic pellets are charged in the drying chambers 11 and magnetrons 12 are operated while the pellets are stirred by stirrers 14 to irradiate the plastic pellets with microwaves to dry the same under heating. After drying, valves 18 are opened to transfer the plastic pellets in the drying chambers 11 to the hopper 100. A heat insulating material is applied to the surface of the hopper 10 to prevent the lowering in the temp. of the plastic pellets. Dried air or inert gas is sent in the hopper 10 from the gas feed port 19 provided to the lower part thereof to prevent the increase in the moisture of the plastic pellets and stable treatment reduced in the variation of residual moisture can be performed.