An aluminum electrolytic capacitor having an excellent short-circuit resistance, high capacitance, long life, and low equivalent series resistance (ESR) is provided. For this purpose, the aluminum electrolytic capacitor includes a capacitor element having a positive electrode foil, a first separator, a negative electrode foil, and a second separator, which are sequentially laminated one on another and wound together. After the capacitor element is impregnated with a driving electrolyte solution and housed in a metallic case, an open end of the metallic case is sealed with a sealing material. A ratio of B/A, i.e. a ratio of total thickness B of the first and second separators after winding with respect to total thickness A of the first and second separators before winding, is set in the range from 0.5 to 0.8.