An object of the present invention is to provide a monoclonal antibody which is useful for treating or diagnosing a disease relating to system ASC amino acid transporter 2 (ASCT2) or a method using the antibody. The present invention provides a monoclonal antibody which specifically recognizes a native three-dimensional structure of an extracellular region of system ASC amino acid transporter 2 (ASCT2) and binds to the extracellular region, or an antibody fragment thereof； a hybridoma which produces the antibody； a DNA which encodes the antibody； a vector which contains the DNA； a transformant obtainable by introducing the vector； a process for producing an antibody or an antibody fragment thereof using the hybridoma or the transformant； and a therapeutic agent using the antibody or the antibody fragment thereof, and a diagnostic agent using the antibody or the antibody fragment thereof.本發明之目的在於提供一種可用於與系統ASC胺基酸轉運蛋白2(ASCT2)相關之疾病之治療及診斷的單株抗體或其使用方法。本發明係關於如下者：特異性識別系統ASC胺基酸轉運蛋白2(ASCT2)之細胞外區域之天然型立體結構且與該細胞外區域結合之單株抗體或該抗體片段、產生該抗體之融合瘤、編碼該抗體之DNA、含有該DNA之載體、導入該載體而獲得之轉形體、使用該融合瘤或該轉形體之抗體或該抗體片段之製造方法、含有該抗體或該抗體片段之治療藥、及含有該抗體或該抗體片段之診斷藥。
