A battery pack including a discharge current interruption FET which cuts off the discharge current, and a minimum voltage detecting portion which switches the discharge current interruption FET from ON to OFF state when the voltage of any battery becomes lower than a minimum voltage. The charge circuit includes a charge current switching portion which switches the charge current so as to charge the battery pack in a main charge mode when the output voltage is higher than a prescribed voltage, and in a preliminary charge mode with a small current when the output voltage is lower than the prescribed voltage. A charge current switching portion charges the battery pack in the preliminary charge mode in the state where the OFF signal of the discharge current interruption FET is provided, even in the state where the output voltage of the battery pack is higher than the prescribed voltage.