Electric power system

An electric power system comprises a plurality of capacitors (101) connected in series, a plurality of DC-AC conversion circuits (102) converting each DC voltage of the plurality of capacitors to an AC signal that an AC component equivalent to the inter-terminal DC voltage of each of the capacitors is superimposed on the respective DC voltages and a plurality of condenser couplers (108) for breaking the respective DC voltages and outputting the AC components respectively, and a processing circuit (104) detecting the inter-terminal DC voltage of the corresponding capacitor from the AC component.