PROBLEM TO BE SOLVED: To provide an inexpensive protein feed for a monogastric stock. SOLUTION: The inexpensive protein feed is obtained by a method of using a biomass of coryneform bacteria as a substitute for fish meal which is the protein feed. When the biomass of the coryneform bacteria subjected to a treatment for improving digestivity of the protein included in the biomass is used, the formulation ratio thereof can be heightened.