To simply produce a fermented material containing a useful microorganism group only in a necessary and sufficient amount even by anyone.

There are provided a drum part forming a top surface opening and a lateral discharging port, a stirring part arranged in the drum part and equipped with stirring blades for mixing a culture liquid with a medium during normal rotation and transporting the medium mixed with the culture fluid toward the lateral discharging port during reverse rotation and a driving part making the stirring part normally and reversely rotate. The stirring part is provided with the plurality of stirring blades mounted on a rotating shaft axially installed in the longitudinal direction so as to pass through the nearly center of the drum part. The stirring blades are formed into a nearly triangular prismatic shape having stirring functional surfaces parallel to the rotating shaft and discharging functional surfaces tilted at a prescribed angle relatively to the rotating shaft.