This invention relates to a monoclonal antibody against a human HIG-1 polypeptide, the antibody binding to at least one epitope included in the amino acid sequence at positions 1-19 of a human HIG-1 polypeptide; an antibody fragment derived from the antibody; a DNA comprising a base sequence encoding a variable region of the antibody; an expression vector comprising the DNA; a cell line producing the antibody; a reagent for detecting a human HIG-1 polypeptide comprising the antibody or the antibody fragment, and a method for detecting a human HIG-1 polypeptide using the antibody or the antibody fragment.