A garbage disposing device 1, comprising a disposing tank 10 of substantially the inverted-conical shape for storing organic substance such as garbage and fermentation accelerator additives in which fermentation microorganism is seeded beforehand in a sealed condition, a rotating shaft 12 which passes vertically through the disposing tank 10 and is driven to rotate by a motor connected to the lower or upper end thereof, a plurality of cutter blades 14 which are fixed in a cantilevered fashion to the rotating shaft 12 at intervals in the vertical direction for grinding and mixing the fermentation accelerator additive and the organic substance, and a plurality of thermo sensors 16 for detecting the temperatures of the disposing tank at a plurality of portions positioned at intervals in the vertical direction. Grinding and mixing can be performed sufficiently with the fact that rotating resistance is small at all vertical positions of the disposing tank 10 because it is formed in the inverted-conical shape and grinding and mixing is performed by a plurality of cutter blades 14 mounted on the rotating shaft 12.