TEST CARTRIDGE

An assay cartridge is an assay cartridge that is attachably and detachably loaded into an immunochromatographic assay apparatus, including a carrier having an assay region in which a color development state changes depending on whether a sample is positive or negative, a case in which the carrier is accommodated, and an opening portion that is provided in the case, is used for observing an observation region LA including the assay region, and is illuminated by a light source in the immunochromatographic assay apparatus, in which at least a part of an inner peripheral wall 18A of the opening portion is a processed surface having an angle of 50° or more with respect to a surface of the observation region LA and having been subjected to a roughening treatment.