An apparatus and method for manufacturing an electricity storage material are provided which allow easily measuring the dissolution rate to solubility of a solution of a powder thickener dissolved in a liquid solvent. An apparatus for manufacturing an electricity storage material includes: a dissolving device that dissolves in a liquid solvent a thickener as powder that is ionized when dissolved; and a dissolution-rate-to-solubility determining device that measures conductivity of the solution produced by the dissolving device and determines a dissolution rate to solubility of the solution based on the measured conductivity. The dissolution rate to solubility can thus be determined without the need to stop the dissolving device during dissolution of the thickener in the liquid solvent. This can significantly improve production efficiency. Since excessive operation of the dissolving device can be prevented, energy saving can be achieved.