An electricity storage device includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte that includes an organic crystal layer including a layered structure and an organic solvent introduced into the organic crystal layer and that is interposed between the positive electrode and the negative electrode to conduct alkali metal ions. The layered structure includes an organic backbone layer containing an aromatic dicarboxylic acid anion having an aromatic ring structure, and an alkali metal element layer containing an alkali metal element that is coordinated with oxygen contained in a carboxylic acid of the organic backbone layer to form a framework. At least one of the positive electrode and the negative electrode adsorbs and desorbs the ions to store and release electric charge.