A protective circuit capable of coping with broad voltage variations of a battery unit to interrupt its charging/discharging current path as damages to the heating unit are prevented from occurrence is disclosed. The protective circuit includes fuses, connected to a charging/discharging current path in series between a battery unit and a charging/discharging control circuit, and a heating unit composed by a series connection of resistors. One of two ends of the resistor which is not connected to the peer resistor is connected to a current path of the fuses. The ends of the resistors not connected to the fuses, are provided with a plurality of terminals selected for connection to a current control element that controls the current flowing through the heating unit, as a range of voltage variations of the battery unit is taken into account.