Pharmaceutical compositions for prevention or treatment of diseases caused by interleukin-6 production, comprising an antibody to interleukin-6 receptor (IL-6R antibody). As the IL-6R antibody, an antibody of animals other than the human such as mice, rats, etc., a chimeric antibody between these and a human antibody, a reshaped human antibody, etc. may be used. The pharmaceutical compositions are useful for prevention or treatment of diseases caused by interleukin-6 production such as plasmacytosis, anti-IgGl-emia, anemia, nephritis, etc.