The present invention provides an antibody specifically against hDlk-1 and having anti-tumor activity in vivo (an anti-hDlk-1 antibody), a fragment of the antibody, a hybridoma that produces the antibody, a complex of the antibody or antibody fragment and an agent, a pharmaceutical composition comprising the antibody and the like, a tumor therapeutic agent, a tumor angiogenesis inhibitor, a tumor diagnostic agent, a method for detecting a tumor, a kit for detecting and/or diagnosing a tumor, etc.