The present invention provides: a humanized anti-HMGB1 antibody that binds specifically to a sequence consisting of an eight-amino-acid residue (EEEDDDDE) at the C terminal of the HMGB1 protein, and that is effective in the treatment or prophylaxis of various inflammatory diseases related to said protein an antigen-binding fragment of said antibody and a pharmaceutical composition including said antibody or said antigen-binding fragment thereof.