PROBLEM TO BE SOLVED: To provide a thickener capable of imparting high viscosity in small amounts, and to provide an external composition containing the thickener.SOLUTION: The thickener contains sodium polyacrylate and a carboxyvinyl polymer, and the external composition contains the thickener. The external composition is preferably a gel agent, a cream agent or an ointment. When the carboxyvinyl polymer is allowed to coexist, it is possible to extremely improve the viscosity by only blending a small amount of the carboxyvinyl polymer.