A charging device is configured with a power supply device and a DC-DC converter that have constant current voltage drooping type overcurrent protection characteristics and that are connected in series. A constant current value in a voltage drooping state of the DC-DC converter is lower than a constant current value in a voltage drooping state of the power supply device. The DC-DC converter is shifted to an operation state to supply a charging current of the constant current value to a charging target when a voltage value of a direct current voltage that is output from the power supply device reaches a maximum output voltage value or an approximate value thereof. Therefore, the charging target can be charged to a higher voltage even though a charging voltage of the charging target is low.