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 anti-B7-H3 antibody via a linker having a structure represented by the following formula: -L1-L2-LP-NH-(CH2)n1-La-Lb-Lc- wherein the antibody is connected to the terminal of L1, and the antitumor compound is connected to the terminal of Lc with the nitrogen atom of the amino group at position 1 as a connecting position.
