The present invention provides a genetic modification non-human organism in which an expression level of Cas9 is high and a plurality of different genes or a plurality of different locations in the same gene can be edited at the same time with high efficiency. The genetic modification non-human organism of the present invention includes a nuclear genome having at least 3 copies of genes that code for Cas9 (CRISPR-associated 9). Egg cells of the present invention are derived from the genetic modification non-human organism having the nuclear genome into which at least 3 copies of genes that code for the Cas9 are introduced. Fertilized eggs of the present invention are obtained by fertilizing the egg cells and sperm derived from the same species of the organism. A method for modifying target genes of the present invention includes a step of introducing a guide RNA into cells derived from the genetic modification non-human organism, the egg cells, or the fertilized eggs.
