PROBLEM TO BE SOLVED: To provide an antibody or an antigen-binding fragment thereof which specifically binds to ErbB3, and use thereof. An antibody or an antigen-binding fragment thereof that specifically binds to ErbB3, comprising a heavy chain complementarity determining region (CDR-H) and a light chain complementarity determining region (CDR-L), wherein a specific amino acid An antibody or an antigen-binding fragment thereof containing CDR-L3 having a sequence, and a pharmaceutical composition for preventing or treating a disease associated with activation or overproduction of ErbB3 protein, comprising the antibody or an antigen-binding fragment thereof. [Selection diagram] None【課題】ＥｒｂＢ３に特異的に結合する抗体またはその抗原結合断片、及びその用途の提供。【解決手段】重鎖相補性決定領域（ＣＤＲ－Ｈ）及び軽鎖相補性決定領域（ＣＤＲ－Ｌ）を含む、ＥｒｂＢ３に特異的に結合する抗体またはその抗原結合断片であって、特定のアミノ酸配列を有するＣＤＲ－Ｌ３を含む抗体またはその抗原結合断片、及び該抗体またはその抗原結合断片を含む、ＥｒｂＢ３タンパク質の活性化または過生成に係わる疾病予防用または疾病治療用の薬学的組成物。【選択図】なし
