PURPOSE: To make packing materials uniform by forming a rotationally symmetrical annular reaction chamber between the inside wall and outside wall of a reaction vessel and making the inside wall and outside wall liquid permeable.

CONSTITUTION: The outside wall 3 of the reaction vessel 1 is enclosed by an upper chamber 9 and a lower chamber 10. The packing materials are fed through an opening 7 into the rotationally symmetrical annular reaction chamber 16 formed between the inside cylinder 2 and the outside wall 3 of the reaction vessel 1. The fluid sent into the reaction chamber 16 is sent through a feed port 17 into the lower chamber 10 and is further made to flow out through the outlet 18 of the upper chamber 9. The packing materials supplied through the opening 7 are dispersed by an agitating arm 8 into the annular reaction chamber 16. A transporting and agitating device 11 formed on the outside surface of the inside cylinder 2 sends the packing material upward by rotation and at this time, the agitating arm 8 agitates the packing material to uniformly distribute the packing materials.