The protective circuit includes a voltage dividing circuit connected in parallel between a first electrode and a second electrode of the unit cell and including a first voltage dividing resistor and a second voltage dividing resistor; a first switching device connected to a junction between the first voltage dividing resistor and the second voltage dividing resistor; a second switching device connected between the junction and the third switching device; and a fourth switching device connected between the junction and the third switching device, wherein, when output voltage of the unit cell becomes equal to or lower than a first reference voltage, the fourth switching device and the first switching device are sequentially turned off, the second switching device is turned on, and the third switching device is turned off, so that voltage output through the first output terminal can be cut off.