PURPOSE: To extract an adsorbent in an adsorbent tank automatically, efficiently, and at low cost and control the adsorbent tank easily.

CONSTITUTION: A plurality of tanks 11a, 11b which are divided by water discharging garrets and have an adsorbent layer composed of an adsorbent, respectively are installed and an adsorbent receiving inlet 31 to receive an adsorbent and an adsorbent extracting outlet 32 to extract the adsorbent are formed respectively in the end part of one tank 11a and in the end part of the other tank 11b. A communication port installed between a plurality of the tanks 11a, 11b and thus the adsorbent is transfered from one tank 11a to the other tank 11b. Also, a means to clean each tank 11a 11b is provided. When air washing or back washing is carried out, the adsorbent in the tanks 11a, 11b gets fluidized and moves between each of the tanks 11a, 11b and replacement of the adsorbent is automatically carried out. In the case the height of the communicating exit 58 is set to be the middle of the normal surfacial height of the adsorbent and the height of the expanded surface at the back washing time, the adsorbent moves through the communicating exit 58 druing the washing.