The present invention provides genetically modified non-human animals which are deficient in at least one or more types of CD3 genes selected from the group consisting of endogenous CD3ε, CD3δ, and CD3γ in its genome and functionally express at least one or more types of human CD3 genes selected from the group consisting of human CD3ε, CD3δ, and CD3γ. In the genetically modified non-human animals of the present invention, mature T cell differentiation and production can take place, and immunocompetent cells including T cells can exert their functions. The genetically modified non-human animals of the present invention enable efficient evaluation and screening in the development of therapeutic agents and therapeutic methods that use human CD3-mediated targeted drugs.
