To remove deposit on a stirrer by sipping the stirrer at the position capable of moving into a cleaning solution in a cleaning solution vessel and stirring to.

When the stirrer 10 is actuated and a circulation belt 11 is rotated, a scoop 11a is brought into dynamic contact with the cleaning solution 24 to be cleaned and is rubber with a brush 25 to remove a stocking organic material 3. The cleaning solution 24 is sucked up by a pump 27 and sprayed to the organic material 3 in fermenting process through a pipe 26 from a spray device 6. The stirrer 10 from which the deposit is removed is moved again on a rail 7 by a driving device 14 to be returned to an operation line and the moving and stirring operation on the operation line is continued. On the other hand, a cover 21 does not disturb the stirring operation of the stirrer 10 by being turned with the operation of an opening and closing devices 22 to close a cleaning solution vessel 20.