In a battery pack, an overcharge detecting circuit compares a voltage between a positive electrode and a negative electrode of a secondary battery with a threshold voltage to detect an overcharge of the secondary battery, and turns off a switching element. A series circuit including a thermistor and a resistor is arranged near the secondary battery and connected in parallel to the secondary battery. A comparator compares a voltage at a junction point of the thermistor and the resistor with a reference voltage corresponding to a predetermined temperature. In response to an output signal of the comparator, a changing unit changes the threshold voltage to a first value when a temperature of the secondary battery is below the predetermined temperature, and changes the threshold voltage to a second smaller value when the temperature of the secondary battery is above the predetermined temperature.