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 following formula: -L 1 -L 2 -L P -NH- (CH 2 ) n 1 -L a -(CH 2 )n 2 -C(=O)- wherein the anti-HER2 antibody is connected to the terminal L 1 , and the antitumor compound is connected to the carbonyl group of the -(CH 2 )n 2 -C(=O)-moiety with the nitrogen atom of the amino group at position 1 as the connecting position.本發明提供一種抗體-藥物結合物作為抗腫瘤效果及安全性面優異之具有優異治療效果的抗腫瘤藥，其特徵為使下式所示的抗腫瘤性化合物與抗HER2抗體，經由下式：-L1-L2-LP-NH-(CH2)n1-La-(CH2)n2-C(=O)-所示的構造之連接物(linker)而結合(抗HER2抗體係於L1之末端結合，抗腫瘤性化合物係將1位之胺基之氮原子作為結合部位，而與-(CH2)n2-C(=O)-部分之羰基結合)。
