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: L 1 -L 2 -L P -NH-(CH 2 )n 1 -L a -L b -L c or -L 1 -L 2 -L P -wherein the anti-HER2 antibody is connected to the terminal L 1 , and the antitumor compound is connected to the terminal L c or L P with the nitrogen atom of the amino group at position 1 as the connecting position.
