A targeting vector was constructed by replacing exon regions in the SGRF gene with appropriate drug marker genes. This vector was transfected into mouse ES cell lines to obtain chimeric mice, which were then crossed with C57BL/6J mice to obtain mice comprising cells in which one SGRF gene alleles was inactivated. By crossing these mice with each other, the present inventors succeeded in producing mice in which both SGRF gene alleles were inactivated. These genetically modified animals can be used to predict the side effects of drugs such as SGRF antagonists.