PURPOSE: To improve the conversion efficiency of soybean into cells useful as feed, food, fertilizer, etc., and to enable the production of bacterial cells at high temperature, by using soybean milk as a main raw material and carrying out mixed culture of bacteria of Bacillus genus and Brevibacterium genus.

CONSTITUTION: Microbial cells are produced by the mixed culture of bacteria of Bacillus genus and Brevibacterium genus in soybean milk used as a main raw material. The soybean milk is produced as a waste liquid, etc., in the production of soybean oil and fat, soya protein, etc., and the milk is used as a raw material and added with an auxiliary nutrient source such as corn steep liquor, rice bran and denucleated yeast. The bacterial strain belonging to Bacillus genus is e.g. Bacillus subtilis (IFO-14132) and Bacillus megatherium (IAM-1166) and the strain belonging to Brevibacterium genus is e.g. Brevibacterium ammoniagenesis (IAM-1041).