A capacitor has a positive electrode, a negative electrode, and a solid electrolyte layer arranged between the electrode layers. At least one of the electrode layers of this capacitor has an Al porous body, and an electrode body held in this Al porous body to polarize the electrolyte. The oxygen content in the surface of the Al porous body is 3.1% by mass or less. The matter that the oxygen content in the surface of the Al porous body is 3.1% by mass or less is equal to the matter that a high-resistance oxide film is hardly formed on the surface of the Al porous body. Thus, this Al porous body makes it possible to make the current collector area of the electrode layer large so that the capacitor can be improved in capacity.