The present invention provides a human artificial chromosome vector comprising a gene encoding the human antibody heavy chain, a gene encoding the human antibody light chain, and a gene encoding IgM heavy chain constant region derived from a nonhuman animal and being capable of producing a human antibody with a higher efficiency when the vector is introduced into an animal. By immunizing the animal produced using a human artificial chromosome vector of the present invention with a desired antigen, a large quantity of human polyclonal antibodies can be supplied.
