An electrochemical capacitor includes electrolytic solution, a capacitor element, and a housing. The electrolytic solution contains cations, anions, solvent formed of materials other than lactones, and a lactone component. The capacitor element includes a negative electrode, a positive electrode, and a separator. The negative electrode includes an electrode layer capable of storing the cations, and the positive electrode includes a polarizable electrode layer and confronts the negative electrode. The separator is disposed between the negative and positive electrodes, and they are layered or wound together. The capacitor element is impregnated with the electrolytic solution. The housing accommodates the capacitor element and the electrolytic solution that contains the lactone component in a quantity ranging from 0.001 wt % to 5 wt % (inclusive) relative to the solvent.