PURPOSE: To contrive the simplification of the apparatus and the improvement of safety, of the dehydrator employed in drying and discarding the laboratory animal subjected to the dosage test for the radioisotope, by installing the cooler for cooling the generated vapor, in the outer circumference of the dehydration chamber equipped with the microwave generator.

CONSTITUTION: The container 11 holding the object A to be dehydrated is placed on the table 12, and the door 8 is closed to seal the dehydration chamber shut. Under this condition, the microwave is generated by the microwave generator 2, and is irradiated upon the object A which is then heated and dehydrated. The generated vapor sticks upon the inner surface of the dehydration chamber 1, is cooled to liquefy by the cooler 3, falls down along the inner surface of the dehydration chamber 1, and is collected in the reservoir 9. Then, the sucking device 4 is actuated to make vacuum the inside of the dehydration chamber 1; hereby, the outflow of the gaseous substance from the dehydration chamber 1 is prevented.