Abstract: The present invention relates to cancer therapies using an antibody that binds to mortalin 2 and a functional nucleic acid. Mortalin expression was found to be upregulated in immortalized cells and tumor tissues. Immortalized human cells highly expressing mortalin showed anchorage-independent growth. When the K antibody, which is a specific anti-mortalin antibody, was injected into a tumor of a nude mouse, tumor growth was suppressed or the tumor shrank compared with the case of a control. In accordance with the present invention, the use of a specific anti-mortalin antibody (K antibody) for tumor therapies and the use of such antibody as a carrier molecule for transportation of immunotoxicin and the like into cells are provided. It has been shown that mortalin can be a target for cancer therapies. In accordance with the present invention, a novel and effective anticancer agent is provided. In addition, an anti-mortalin antibody that is internalized by cells is developed.