The present invention has for its object to provide a G0 transgenic chimera bird which is introduced an antibody gene with a replication-defective retrovirus vector, and produces an antibody by expressing the transgene a production method of an antibody which comprises recovering the antibody expressed by the produced G0 transgenic chimera bird and a production method of a G0 transgenic chimera bird which comprises incubating a bird fertile egg, and injecting an embryo after and exclusive of a period immediately after the start of incubation with a retrovirus vector.That is, the present invention relates to a G0 transgenic chimera bird which is introduced an antibody gene with a replication-defective retrovirus vector, and produces an antibody by expressing a transgene.
