To provide a nonhuman mammal having DNA integrated with an alien thyroid hormone receptor gene (modifier gene) and useful for elucidating a critical mechanism of a thyroid hormone insensitiveness and as a curing model and for screening of a therapeutic agent of a disease of the thyroid.

This nonhuman mammal of a rodent, etc., such as a mouse or a rat having DNA integrated with an α- or a β-type, etc., of alien thyroid receptor gene (modifier gene) is utilized for elucidating a pathological state mechanism of a hyperthyroidism, a Basedow disease, a thyroiditis, a goiter and a thyroid cancer, etc. Preferably, a gene therapy of a disease of the thyroid containing a thyroid hormone insensitiveness is performed by using a vector containing the alien thyroid hormone receptor gene (modifier gene) and capable of manifesting in a mammal.