To provide an organic matter treating agitation device suited for decomposition treatment of organic matter.

A device main body 2 of an organic matter treating agitation device 1 is constituted of a cylindrical peripheral wall part 3 horizontally arranged and right and left side face parts 4, 5 closing both the end parts of the peripheral wall part 3 to form a cylindrical housing space 6 in which marine products such as blue mussels are housed together with microorganisms and bacteria beds. The peripheral wall part 3 is provided with a feeding port 7 and a discharge part 8 in the right end part and in the left end part thereof respectively. Screws 11, 11 extending in the right and left directions are installed in the device main body 2 and both the end parts of the screw 11 are rotatably supported on right and left revolving shafts 14, 15. Both the revolving shafts 14, 15 are freely rotatably supported in the central parts of the right and left side face parts 4, 5 to enable the revolution of the screws 11, 11 to rotate along the inner periphery of the peripheral wall part 3. The right revolving shaft 15 is connected to a driving device 16 and by the driving device 16, the right revolving shaft 16 and the screws 11 are rotated and driven.