BST2 antibodies were selected by using as an indicator the binding between BST2 antibodies and various splicing variants of human BST2 antigen. As a result, the present inventors successfully obtained BST2 antibodies that specifically recognize BST2D, which has been reported to be expressed at high levels in cancer cells. The antibodies of the present invention specifically bind to cells expressing BST2D. Non-specific antibody binding to non-target tissues, which results in the decrease of antibody concentration in blood, can be prevented by using the antibodies of the present invention therapeutically. Alternatively, the present invention provides diagnostic agents comprising an antibody of the present invention, which specifically detect tissues expressing BST2D.