The present invention provides a screening method for a compound capable of inducing regulatory T cells, comprising the following steps:(1) a step for culturing CD4+ T cells having a naïve phenotype in the presence of a test compound, and isolating T cells from the culture product; (2) a step for evaluating the immunosuppressive function of the T cells isolated in the step (1); (3) a step for obtaining the foregoing test compound as a compound capable of inducing regulatory T cells if the results of the evaluation in the step (2) show that the T cells isolated in the step (1) have immunosuppressive function. The present invention also provides a method of producing regulatory T cells, comprising culturing CD4+ T cells having a naïve phenotype in the presence of a rapamycin compound to obtain regulatory T cells. The regulatory T cell produced by the method can be used as an immunomodulator for the prophylaxis or treatment of the rejection in organ transplantation, an allergic disease, an autoimmune disease, a graft-versus-host disease (GVHD), infertility and the like.