A knockin nonhuman animal having a DNA wherein a region containing at least an exon of an MnSOD gene is interposed between two recombinase recognition sequences is disclosed. Further, a knockout nonhuman animal obtainable by mating a transgenic nonhuman animal expressing a recombinase in a specific tissue with the above knockin nonhuman animal, wherein an expression of manganese superoxide dismutase in the specific tissue is suppressed or deficient; and a nonhuman animal obtainable by further mating one of the above animals with the above knockout nonhuman animal, wherein manganese superoxide dismutase is specifically deficient in the specific tissue are disclosed.