As an antitumor drug which is excellent in terms of antitumor effect and safety and has an excellent therapeutic effect, there is provided an antibody-drug conjugate in which an antitumor compound represented by the following formula is conjugated to an anti-HER2 antibody via a linker having a structure represented by the formula: L1-L2-LP-NH-(CH2)n1-La-Lb-Lc or -L1-L2-LP-wherein the anti-HER2 antibody is connected to the terminal L1, and the antitumor compound is connected to the terminal Lc or LP with the nitrogen atom of the amino group at position 1 as the connecting position.
