Abstract: A power supply device includes a solar battery configured to generate electric power by light and output the electric power, a secondary battery cell configured to store the electric power, a battery management unit configured to perform a protection operation by cutting off the extraction of the electric power stored in the secondary battery cell when a storage voltage of the secondary battery cell is equal to or less than a protection voltage, and an automatic recovery control unit that is connected between the solar battery and the battery management unit and configured to perform a recovery charging operation by converting a portion of the electric power output from the solar battery into a first voltage and a first current value and supplying the electric power to the battery management unit even when the battery management unit is in an operation stop state.