PROBLEM TO BE SOLVED: To provide a novel thickner useful for surfactants, especially acylamino acid-based anionic surfactants, and to provide a detergent composition not providing slimy feeling in use and providing moist feeling after use.SOLUTION: There is provided a thickner for surfactants represented by the formula (1). (1), where M represents a hydrogen atom, an alkali metal atom, a 1/2 alkaline earth metal atom, ammonium, organic ammonium, an amino acid, an amino acid alkali metal salt, taurine, an alkali metal salt of taurine, N-methyl taurine or an alkali metal salt of N-methyl taurine.
