[PROBLEMS] To provide an antitumor drug having an excellent therapeutic effect and excellent antitumor effect and safety. An anti-tumor compound represented by the following formula: and an anti-HER3 antibody are represented by the following formula: -L1-L2-LP-NH- (CH2) n1-La- (CH2) n2-C (= O)-or -L1-L2-LP- An antibody-drug conjugate characterized by being linked through a linker having a structure represented by (anti-HER3 antibody binds at the end of L1, The compound provides a bond to the carbonyl group of the — (CH 2) n 2 —C (═O) — moiety or to the C terminus of LP using the nitrogen atom of the amino group at position 1 as the binding site. [Selection figure] 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：【化１】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（抗ＨＥＲ３抗体はL1の末端において結合し、抗腫瘍性化合物は、１位のアミノ基の窒素原子を結合部位として、-(CH2)n2-C(=O)-部分のカルボニル基に又はLPのＣ末端に結合する）を提供する。【選択図】なし
