An object of the present invention is to provide a nonhuman model animal of Th2-mediated hyperimmune response lacking PIR-B gene function on its chromosome by which the Th2-mediated immune response mechanism and allergy onset mechanism in vivo can be analyzed and which is liable to suffer from not only hyper-response of B cells but also allergy, and an inducer/promoter or an inhibitor for Th2-mediated immune response, etc. with the use of the nonhuman model animal of Th2-mediated hyperimmune response. The nonhuman model animal of Th2-mediated hyperimmune response is prepared by integrating a fragment comprising exons 1 to 7 and the domain in the 5' side of exon 8 of mouse PIR-B gene and another fragment containing exons 10 to 14 into a vector pMC1-Neo, cleaving it with Xho I-Sal I, integrating it into a vector pIC19R-MC1tk having herpes virus thymidine kinase to thereby construct targeting vector, transferring the targeting vector into ES cells and then injecting the ES cells into blastcyst.