An objective of the present invention is to provide an antibody having a high cell death-inducing activity. To solve the above-described problems, the present inventors immunized mice with cells expressing human HLA class IA and human .beta.2 microglobulin (.beta.2M) to obtain monoclonal antibodies. Screening of the obtained antibodies was performed to obtain ten clones of antibodies having a cell death-inducing activity. Analyses of these clones revealed that three of the clones (antibodies C3B3, C11B9, and C17D11), which have the .alpha.2 domain of the HLA class I antigen as an epitope, showed a stronger cytotoxic activity when crosslinked with an anti-mouse IgG antibody. Furthermore, when a C3B3 diabody was generated, this diabody was revealed to show a stronger anti-tumor effect compared with conventional diabodies of the 2D7 antibody, which is an HLA class IA antibody.