The present invention provides a method of enhancing an efficiency of homologous recombination when a gene encoding a desired protein known or unknown in terms of function is introduced into a genome of a pluripotent cell such as ES cell. More particularly, the present invention relates to: a non-human animal-derived pluripotent cell comprising a foreign enhancer at a site downstream of an immunoglobulin gene on chromosome; a non-human animal pluripotent cell comprising a gene, which encodes a desired protein at a site downstream of the immunoglobulin gene and upstream of the foreign enhancer on the chromosome, said gene being in an overexpressible state; a method of establishing said pluripotent cell; and a chimeric non-human animal and its progeny produced by use of the pluripotent cells and a method of producing the same. The present invention further relates to a method of analyzing the function of a desired protein or a gene encoding the protein by comparing a phenotype of the chimeric non-human animal or its progeny with that of a control animal, and/or to a method of producing a useful protein by use of the chimeric non-human animal or its progeny.