PURPOSE: To extend the service life of a carrying device and simplify both the constitution of the apparatus and the controlling manipulation by providing doors on a truck in a setup for these doors to open and close the opening of a main casing and load the truck with material for the drying and unload it at one side of the main casing.

CONSTITUTION: After the cleaning has been finished, a carrying device 16 is moved to bring a carrying bucket 15 over an unloading place of a drying station 13. On the other hand, a truck 20a is brought out through an opening 21 to a position outside the main casing 18 beforehand. Now the carrying bucket 15 is laid on the truck 20a. Then the opening 21 of the main casing 18 is closed from inside by an inner door 23b provided at the other side of the truck 20a. After laying of the carrying bucket 15, the truck 20a is inserted into the main casing 18; with this insertion, an outer door 23a provided at one side of the truck 20a closes the opening 21 of the main casing 18 from outside. This constitution makes it unnecessary to provide an additional driving means to open and close the opening 21 of the main casing 18.