To provide: a water-soluble amphoteric copolymer having excellent hydrophilicity and high adsorption capability, and capable of exhibiting dramatically excellent dispersibility even under high hardness conditions and being preferably used in a detergent composition application, for example; an application thereof; and a production method of such a water-soluble amphoteric copolymer. A water-soluble amphoteric copolymer produced by a copolymerization of a monomer component comprising a cationic monomer (a), an anionic monomer (b), and an unsaturated polyalkylene glycol monomer (c), wherein the monomer (b) is a carboxyl group-containing monomer and/or a sulfonic acid group-containing monomer (d), and the monomer (b) is more than 50% by mole relative to 100% by mole of a total amount of the monomers (a), (b), and (c) if the monomer (b) consists of the carboxyl-group containing monomer, and at least one species of monomer among the monomers (a), (d), and (c) is 30% by mole or less relative to 100% by mole of a total amount of the monomers (a), (d), and (c) if the monomer (b) comprises the sulfonic acid group-containing monomer (d).