A test kit for detecting a substance to be detected contained in a liquid sample by allowing the liquid sample to develop in a developing direction, the test kit comprising: a first member, which contains a region in which is held a labeling substance with a label immobilized on a substance that specifically binds with the substance to be detected, and a second member, which has a detection zone where the labeling substance is captured through the substance to be detected, which is connected downstream of the first member in the developing direction, and which allows the labeling substance contained in the liquid sample that flows in from the first member, to develop into the detection zone, wherein the first member has: a dropping region located furthermost upstream and containing a portion onto which the liquid sample is dropped, characterized in that the test kit further comprises a labeling substance holding region connected to the second member and having a containing portion that contains the labeling substance and a non-containing portion that is located upstream of the containing portion and that does not contain the labeling substance, and a backflow prevention region, which is connected between the dropping region and the non-containing portion of the labeling substance holding region, and in which absorbency is set higher than in the dropping region and the labeling substance holding region. a first member, which contains a region in which is held a labeling substance with a label immobilized on a substance that specifically binds with the substance to be detected, and a second member, which has a detection zone where the labeling substance is captured through the substance to be detected, which is connected downstream of the first member in the developing direction, and which allows the labeling substance contained in the liquid sample that flows in from the first member, to develop into the detection zone, wherein the first member has: a dropping region located furthermost upstream and containing a portion onto which the liquid sample is dropped, characterized in that the test kit further comprises a labeling substance holding region connected to the second member and having a containing portion that contains the labeling substance and a non-containing portion that is located upstream of the containing portion and that does not contain the labeling substance, and a backflow prevention region, which is connected between the dropping region and the non-containing portion of the labeling substance holding region, and in which absorbency is set higher than in the dropping region and the labeling substance holding region. a dropping region located furthermost upstream and containing a portion onto which the liquid sample is dropped, characterized in that the test kit further comprises a labeling substance holding region connected to the second member and having a containing portion that contains the labeling substance and a non-containing portion that is located upstream of the containing portion and that does not contain the labeling substance, and a backflow prevention region, which is connected between the dropping region and the non-containing portion of the labeling substance holding region, and in which absorbency is set higher than in the dropping region and the labeling substance holding region.