Electricity accumulating device

An electricity accumulating device includes capacitors connected in series, balanced voltage adjusting portions connected to the capacitors respectively, and a control circuit connected to the balanced voltage adjusting portions. The control circuit performs the following operations: measuring two voltages at different times from each other across each capacitor during the non-charge-or-discharge period of the capacitors by using the balanced voltage adjusting portions; calculating the absolute value of the difference between the two voltages; determining the balanced voltage of each of the capacitors according to the absolute value; and controlling the balanced voltage adjusting portions to make the voltage across each capacitor a balanced voltage.