PURPOSE: To convert an organic waste into a digested or odorless dried useful material and give fertilizer and other useful materials, by inoculating the organic waste with bacillus stearothermophilus and carrying out cultivation in the presence of ferrous sulfate.

CONSTITUTION: An organic waste, preferably poultry manure, hog manure, human waste, similar materials or an organic waste containing them is inoculated with thermophilic Bacillus stearothermophilus (FERM-P No.7587) and mixed therewith. Ferrous sulfate is then added to the organic waste, and cultivation is carried out at a high temperature, preferably 40W70°C with aeration to give an odorless dried useful material. The amount of the above-mentioned ferrous sulfate to be added is preferably 1/1,000W1/10,000 the weight of the organic waste in the initial period of the cultivation.