To efficiently enable materials to be treated such as dirt and trash to be decomposed of by enhancing the function of microorganisms implanted to chips.

A damming plate is fixed on the inner surface of a treating vessel 5 above an agitator blade 6 in such a way to horizontally project toward the center part of the treating vessel 5. The damming plate 26 dams temporarily the chips 7 and the dirt 27 pushed to the front face side in a rotational direction by the agitation blade 6. The agitation blade 6 forms a depressed part by pushing the chips 7 and the dirt 27 in the rotating direction in the back face side of the damming plate 26 (or the front face side in the case of a small amount of the chips), makes the dammed chips 7 and dirt 27 climb over (or before climbing over) the damming plate 26 and fall into the depressed part 36, and prevents the generation of lumps which will be generated in the course of agitation of the chips 7 and the dirt 27 by the agitator blade 6. The sufficient decomposition of the dirt 27 can be realized by enhancing the function of the microorganisms by agitation while aerating the chips 7 and the dirt 27.