The present invention provides: a novel antigen of an allergy to eggs; a diagnostic method and a diagnostic kit for an allergy to eggs; a pharmaceutical composition including said antigen; eggs, egg products or chickens from which said antigen is removed or reduced, the chickens laying said eggs or being born from said eggs; a method for manufacturing egg products from which said antigen is removed or reduced; and a tester for determining whether an egg antigen is present in a subject. The present invention also relates to: a polypeptide including an epitope of an antigen; a diagnostic kit, a diagnostic composition, and a diagnostic method for an allergy, in which said polypeptide is included; a pharmaceutical composition including said polypeptide; and a raw material or a product from which the antigen is removed or reduced and which includes said polypeptide. Furthermore, the present invention relates to a tester for determining whether an antigen is present in a subject.
