An electric storage device, comprising: an input terminal; a direct current power source connected to the input terminal; a charge element connected to the input terminal and limiting a direct current from the direct current power source; a charging current detection unit connected to the charge element and adapted to detect a charging current; a plurality of storage elements (102C, 104C, 106C) connected to the charging current detection unit, said storage elements being connected in serial or in series parallel connection; a discharge element connected to the plurality of storage elements; an output terminal connected to the discharge element; a voltage detection unit configured to detect the entire voltage of the plurality of storage elements (102C, 104C and 106C) or at least one of the inter-terminal voltages of the plurality of storage elements (102C, 104C and 106C); the inter-terminal voltage being the voltage across each storage element; a control unit connected to the voltage detection unit and controlling the charge element and the discharge element; a voltage comparison unit connected to the voltage detection unit and the control unit; characterized in that the electric storage device further comprises a variable reference voltage source connected to the voltage comparison unit, and its magnitude is adjusted therefor, wherein the magnitude of the variable reference voltage source is adjusted so as to be higher at an initial stage of charging compared to the magnitude of the reference voltage at a subsequent stage of charging, based on an element of the group comprising: - a charging current value detected by the charging current detection unit; - a temperature of at least one of the storage elements or an ambient temperature of a position where the storage elements are placed; - a time measured by a timer circuit connected to the control unit; - differences of the inter-terminal voltages of the storage elements before and after a halt of the charging, said charging of the storage elements being temporarily halted during the charging; wherein, when a detection signal taken out of the voltage detection unit exceeds the variable reference voltage source, an overvoltage is detected and the charge element is controlled through the control unit to halt the charging current or to limit a magnitude of the charging current, so as to prevent deterioration of at least one of the plurality of storage elements. an input terminal; a direct current power source connected to the input terminal; a charge element connected to the input terminal and limiting a direct current from the direct current power source; a charging current detection unit connected to the charge element and adapted to detect a charging current; a plurality of storage elements (102C, 104C, 106C) connected to the charging current detection unit, said storage elements being connected in serial or in series parallel connection; a discharge element connected to the plurality of storage elements; an output terminal connected to the discharge element; a voltage detection unit configured to detect the entire voltage of the plurality of storage elements (102C, 104C and 106C) or at least one of the inter-terminal voltages of the plurality of storage elements (102C, 104C and 106C); the inter-terminal voltage being the voltage across each storage element; a control unit connected to the voltage detection unit and controlling the charge element and the discharge element; a voltage comparison unit connected to the voltage detection unit and the control unit; characterized in that the electric storage device further comprises a variable reference voltage source connected to the voltage comparison unit, and its magnitude is adjusted therefor, wherein the magnitude of the variable reference voltage source is adjusted so as to be higher at an initial stage of charging compared to the magnitude of the reference voltage at a subsequent stage of charging, based on an element of the group comprising: - a charging current value detected by the charging current detection unit; - a temperature of at least one of the storage elements or an ambient temperature of a position where the storage elements are placed; - a time measured by a timer circuit connected to the control unit; - differences of the inter-terminal voltages of the storage elements before and after a halt of the charging, said charging of the storage elements being temporarily halted during the charging; - a charging current value detected by the charging current detection unit; - a temperature of at least one of the storage elements or an ambient temperature of a position where the storage elements are placed; - a time measured by a timer circuit connected to the control unit; - differences of the inter-terminal voltages of the storage elements before and after a halt of the charging, said charging of the storage elements being temporarily halted during the charging; wherein, when a detection signal taken out of the voltage detection unit exceeds the variable reference voltage source, an overvoltage is detected and the charge element is controlled through the control unit to halt the charging current or to limit a magnitude of the charging current, so as to prevent deterioration of at least one of the plurality of storage elements.