A pharmaceutical composition and a treatment method, each of which is characterized in that an antibody-drug conjugate and an immune checkpoint inhibitor are administered in combination, wherein the antibody-drug conjugate is formed by bonding a drug linker represented by formula (1) (wherein A represents an antibody-bonding position) to an antibody through a thioether bond； and a pharmaceutical composition and a treatment method, each of which is characterized in that the antibody-drug conjugate is contained and is also characterized by being used for the treatment of a disease that can be ameliorated through an anti-tumor immunity activation effect.
