The present invention provides an experimental model animal which does not develop anaphylaxis, a type I allergy, can specifically induce Arthus reaction, a type III allergy, is not affected by type I allergy and evaluates type III allergy inflammation individually, and a method of screening a reaction accelerating or inhibitory substance in a type III allergy reaction through Fc.gamma.RIII by using said experimental model animal. In order to eliminate Fc.gamma.RIIB that demonstrates suppressive action to response through Fr.gamma.RIII, a mouse wherein the deletion mutation of both molecules of Lyn and Fc.gamma.RIIB are homozygotic (Lyn.sup.-IIB.sup.-) was generated by mating Lyn knockout mouse (Lyn.sup.-/-) and Fc.gamma.RIIB knockout mouse (Fc.gamma.RIIB.sup.-/-), and was used to measure and evaluate the deficiency of Fc.gamma.RIII function in systemic passive anaphylaxis and the reduction of Fc.gamma.RIII function in a bone marrow-derived mast cell, or the like.