Almost all types of idiopathic inflammatory myopathy (IIM) are treated by immune-modulating therapies. Corticosteroids, such as prednisolone and methylprednisolone, are used as first-line therapy for IIM. When the symptoms cannot be sufficiently improved, immunosuppressive agents, such as azathioprine, methotrexate, or tacrolimus, should be administered approximately two weeks after starting corticosteroid therapy. Moreover, intravenous immunoglobulin is recommended for severe cases at the same time as starting immunosuppressive agents. If these therapies do not improve symptoms, biologics, such as rituximab, should be introduced. Once IIM is controlled with immuno-modulating therapies, the drugs should be gradually tapered to avoid exacerbating the symptoms.