Adherent foreign matters such as metal powders and sludges are removed from the surface of work pieces of metal, ceramics or the like in a treating process thereof. Work pieces where foreign matters adhere and a granules composed of a heat-resisting inorganic substance such as sand are put together into a container. The inside of the container is heated to raise the temperature to the melting point of the adherents or to a temperature near it, and an external force is applied; to the container so that the work pieces will move in the container, for example, to rotate the container.