Provided is a novel therapeutic agent for autoimmune diseases, particularly type 1 diabetes and rheumatoid arthritis.A novel therapeutic agent for autoimmune diseases (type 1 diabetes and rheumatoid arthritis) based on a new action mechanism can be provided by producing a novel anti-CD98 antibody and using same. The novel anti-CD98 antibody does not inhibit amino acid transport of CD98 and, different from known anti-CD98 antibody, further has actions such as a suppressive action on T lymphocyte activation, a suppressive action on cell adhesion mediated by fibronectin, as well as an OVA antibody production suppressive action in OVA immunization model and the like.
