The present invention is based on the discovery that CLDN 18.2, including stomach cancer, esophageal cancer, pancreatic cancer, lung cancer, ovarian cancer, colon cancer, liver cancer, head and neck cancer, and cancer of the gall bladder, CLDN 18.2 antibody-drug conjugate which is effective in treating and / or preventing cancer diseases associated with cells expressing the anti-CLDN 18.2 antibody.本発明は、胃がん、食道がん、膵がん、肺がん、卵巣がん、大腸がん、肝がん、頭頸部がん、及び胆嚢のがん、並びにこれらの転移を含めた、CLDN18.2を発現する細胞と関連したがん疾患を処置及び/又は予防するのに有効である抗CLDN18.2抗体-薬物コンジュゲートを提供する。