Problem: An object is to achieve a charging/discharging circuit using an element with low voltage endurance, and to provide a charge storage system, the charging/discharging circuit and a utility interconnection device at low cost. Solution: A charge storage system 3 includes: a storage 30; and a charging/discharging circuit 31 configured to perform charging and discharging of the storage 30 via a transformer 40. The charge storage system 3 is connected to a device configured to convert DC power output from a DC power supply 1 into AC power and configured to output the converted AC power, and is configured to charge the DC power into the storage 30. The transformer 40 includes: a power source-side winding 41 to which the DC power is input; and a storage-side winding 51 connected to the storage 30, and the charging/discharging circuit 31 is configured to change a turn ratio between the power source-side winding 41 and the storage-side winding 51 (= (the number of turns of the power source-side winding 41)/(the number of turns of the storage-side winding 51)) such that the turn ratio at the charging of the storage 30 is larger than the turn ratio at the discharging of the storage.
