IgG4-related disease (IgG4-RD) is a new concept which is characterized by elevated serum IgG4 level and infiltration of IgG4+ plasma cells in target tissues. IgG4-RD can involve various organs including skin as well. The cutaneous features of IgG4-RD are not characteristic, but are known as pruritic multiple erythematous nodules or plaques. We report a case which was considered as erythema multiforme initially, but later diagnosed as IgG4-RD. A 64 year-old female had erythematous patches and papules with pruritus on her whole body. The skin lesion appeared 10 days before and exacerbated since then. She also had oral mucosal swelling, intermittent sorethroat and epigastric pain that could not be diagnosed at the departments of otorhinolaryngology and gastroenterology. Serum IgG4 level was elevated, and diffuse enlargement of pancreas with mild peripancreatic infiltration was shown. In this study, we report a IgG4-RD patient who showed dramatic improvement after receiving treatment with systemic steroid, even if no definite diagnosis was made with pathologic studies.