A capacitor includes a capacitor element and an electrolyte containing a lactone compound. At least one of a positive electrode and a negative electrode of the capacitor element contains activated carbon Entire surface functional group amount D (meq/g/nm2) in an average sectional area of pores of the activated carbon is calculated at 0.152 or less by the following equation: D=F/S where F represents an entire surface functional group amount per unit weight (meq/g) of the activated carbon, and S represents an area (nm2) of a circle of which diameter is an average diameter of the pores of the activated carbon.