PROBLEM TO BE SOLVED: To provide an antitumor drug having an excellent therapeutic effect, which is excellent in antitumor effect and safety. SOLUTION: An antitumor compound represented by the following formula: and an anti-HER3 antibody are combined with the following formula: -L1-L2-LP-NH- (CH2) n1-La- (CH2) n2-C (= O). -Or-An antibody-drug conjugate characterized by binding via a linker of the structure represented by L1-L2-LP-. [Selection diagram] None【課題】抗腫瘍効果と安全性面に優れる、優れた治療効果を有する抗腫瘍薬の提供。【解決手段】次式：で示される抗腫瘍性化合物と抗ＨＥＲ３抗体とを、次式：-L1-L2-LP-NH-(CH2)n1-La-(CH2)n2-C(=O)-又は-L1-L2-LP-で示される構造のリンカーを介して結合させたことを特徴とする抗体－薬物コンジュゲート。【選択図】なし
