The present invention provides a humanized anti-HMGB1 antibody which specifically binds to a sequence consisting of the C-terminal 8 amino acid residues (EEEDDDDE) of HMGB1 protein and is effective for treatment or prevention of various inflammatory diseases related to this protein, as well as an antigen-binding fragment thereof. The present invention also provides a pharmaceutical composition comprising such an antibody or antigen-binding fragment thereof.