Provided is a capacitor in which, even in the case of a high maximum charging voltage, decomposition of the electrolyte can be suppressed and charging and discharging can be performed with stability. The capacitor includes a positive electrode containing a positive-electrode active material, a negative electrode containing a negative-electrode active material, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive-electrode active material contains a porous carbon material, in a volume-based pore size distribution of the porous carbon material, a cumulative volume of pores having a pore size of 1 nm or less accounts for 85% or more of a total pore volume, the porous carbon material has a crystallite size of 1 to 10 nm, the porous carbon material contains an oxygen-containing functional group, and a content of the oxygen-containing functional group is 3.3 mol % or less.