A target substance detection element that can effectively prevent the nonspecific adsorption of a target substance or impurities and detects the target substance with high sensitivity, a target substance detection kit, and a structure constituting the target substance detection element. The structure has a substrate, polymers present on the substrate surface, and first target substance capturing molecules bonded to the polymers. The polymer is composed of a polymer of a carboxybetaine monomer represented by General Formula (1) below. The first target substance capturing molecules are bonded to some of the carboxyl groups of the polymers. A compound represented by General Formula (2) is bonded to at least some of the carboxyl groups, from among the carboxyl groups of the polymers, that arenot bonded to the first target substance capturing molecules.