A charging device is provided, which is capable of starting up a control circuit without any separate power supply so as to start an appropriate charge operation even when a secondary battery is in an overdischarged state. A charging device to charge a secondary battery with electric power generated by a solar cell includes: a charging control unit that controls the electric power generated by the solar cell to have a current value and/or a voltage value suitable for charging, and that supplies the controlled electric power to the secondary battery; and a start-up control unit that supplies, to the charging control unit, a boosted power source by boosting the electric power from the solar cell when charging is started, and that starts up the a charging control unit.