To provide a compact and easily maintainable device for performing biological treatment mainly to solid matter separated in a flush toilet.

In the biological treatment device comprising: an outer shell for prescribing a substantially hermetically sealed space; an opening for charging excrement or the like provided to the outer shell; a stirring means provided in the space; and an opening for discharging the excrement or the like after the treatment provided at the outer shell, the stirring means is characterized in that the contents are stirred and moved to different directions in the central part and the peripheral part in the space, and the contents are circularly stirred in the space.