An electric double-layer capacitor has an electrolyte solution and an element constructed of a positive electrode and a negative electrode which are each composed of a current collecting substrate and an active material composition, and a separator situated between the positive and negative electrodes. When the element is in place within the capacitor, the portion of the separator sandwiched between the active material compositions of the respective electrodes has a pore volume which is at least 0.4 times the total pore volume of the positive and negative electrodes. This construction enables the separator to hold the electrolyte solution required by the electrodes for charging and discharging, thus endowing the capacitor with a high capacitance and a long cycle life.