A power supply device includes an electric storage unit connected to a main power supply and a load via a charging circuit; and a control circuit connected to the main power supply, the charging circuit, a voltage detection circuit, and a current detection circuit. When the electric storage unit is charged up to a steady-state voltage Vcs of the electric storage unit, the control circuit controls the electric storage unit to be charged until the voltage Vc of the electric storage unit reaches a voltage for determining the property deterioration of the electric storage unit. During the charge process, the control circuit calculates at least one of the internal resistances and the capacitance of the electric storage unit to determine the property deterioration of the electric storage unit.