The present invention provides a method of producing a non-human vertebrate that harbours germ cells having a desired gene transferred thereto, comprising injecting the desired gene to the testis of a non-human vertebrate wherein no tight junction exists between Sertoli cells to transfer the desired gene to germ cells, so as to obtain a non-human vertebrate that harbours the germ cells having the desired gene transferred thereto. Using the method of the present invention, even in animal species and lines for which in vitro transduction has been difficult to date, it is possible to obtain an individual harbouring germ cells, particularly spermatogonial stem cells, having a desired gene transferred thereto, at extremely high efficiency. Also, the fertility of the male to receive an injection of the gene is retained, compared to in vitro transduction of germ cells, because gene transfer is achieved without reducing the number of spermatogonial stem cells in the testis and transgenic sperms and transgenic animals can easily be prepared.