Abstract: The present application discloses an antigenic detector, including: a pen holder and a pen cap. The pen holder includes: a test paper tube, a test paper assembled in the test paper tube, a test paper support, and a foam support installed on the front end of the test paper tube with a foam and a protective cover; the pen cap includes: a base, an aluminum foil assembled in the base, and an interior of the base forms a cavity into which a front end of the pen holder is inserted, and a reaction solution is sealed inside the cavity of the base by the aluminum foil; the protective cover is detachably installed on the front end of the test paper tube and covers the foam; the foam support is provided with a channel that communicates with an interior of the test paper tube.