An electric power system comprises a plurality of capacitors connected in series, a plurality of DC-AC conversion circuits converting each DC voltage of the plurality of capacitors to an AC signal having an AC component equivalent to the inter-terminal DC voltage of each of the capacitors superimposed on the respective DC voltages, a plurality of condenser couplers break the respective DC voltages and output the AC components respectively, and a processing circuit detecting the inter-terminal DC voltage of the corresponding capacitor from the AC component.
