A capacitor includes a metal case and a terminal plate. The metal case accommodates a capacitor element together with a driving electrolyte and is joined to one of the electrodes of the capacitor element at its inner bottom surface. The terminal plate is joined to the other electrode at its inner surface so as to seal the opening of the metal case. The terminal plate is provided with a pressure regulating valve also functioning as a driving-electrolyte filling hole. The pressure regulating valve includes a ring-shaped elastic member which is pressed into the wall formed on the terminal plate.