PURPOSE: To separate a foreign material effectively with a simple constitution by supporting a filter element on an axis rotatably as well as providing an outlet joint inserted between a raw material gas chamber and a clean gas chamber in a state closed by a separation wall.

CONSTITUTION: A filter element 8 is arranged in a housing 1 separated into a raw material gas chamber 3 and a clean gas chamber 4 by a separation wall 2. The filter element 8 has two perforated walls 10 separated from each other, while the perforated walls 10 limits a circular filter bed filled with carbon particles by a closed front side. The filter element 8 is supported rotatably on an axis and is provided with an outlet joint 15 arranged so as to penetrating a separation chamber 2 in a sealed state between a raw material gas chamber 3 and a clean gas chamber 4.