Abstract: [Problem] It is desired to develop an antibody-drug conjugate capable of being systemically administered and delivering a STING agonist specifically to a target cells or organ (for example, a tumor lesion), and a therapeutic agent and/or therapeutic method using the antibody-drug conjugate for diseases related to STING agonist activity, for example, diseases (for example, cancers) to which immunostimulation therapy can be applied. [Solution] The present invention provides a novel antibody-CDN derivative conjugate which can be systemically administered and exhibits an antitumor effect against an antigen-expressing tumor.