As an antitumor drug which is excellent in terms of antitumor effect and safety, there is provided an antibody-drug conjugate in which an antitumor compound represented by the following formula is conjugated to an antibody via a linker having a structure represented by the following formula: -L 1 -L 2 -L P -NH-(CH 2 )n 1 -L a -L b -L c -wherein the antibody is connected to the terminal of L 1 , and the antitumor compound is connected to the terminal of L c with the nitrogen atom of the amino group at position 1 as a connecting position.