Provided is a prophylactic agent for an autoimmune disease, comprising a fraction of a milk-derived basic protein, lactoperoxidase, and lactoferrin as active ingredients. The agent can be taken on a daily basis, and even if it is taken over a long period of time, its safety is high, and hence, an autoimmune disease such as type I diabetes mellitus or rheumatoid arthritis, which could not be effectively prevented or treated by a conventional method, can be prevented.
