A remaining battery capacity measuring device having a microprocessor and an integrated circuit is packaged together with a secondary battery to form a battery pack. The integrated circuit includes a current measuring circuit for charging and discharging currents of a secondary battery, an overcurrent detection circuit for detecting overcurrent in the secondary battery, a driver circuit for driving a semiconductor switch for change and discharge control of the secondary battery, and a power switch circuit for power-saving operation. The current measuring circuit includes an operational amplifier for detecting a voltage across a resistor for current detection, and has a function to apply a variable offset voltage to the amplifier and a function to vary the gain of another operational amplifier for amplifying the output of the former operational amplifier. The current measuring circuit detects the voltage across the resistor independently of the overcurrent detection circuit, and enjoys high measurement accuracy. The overcurrent detection level and overcurrent detection response time of the overcurrent detection circuit can be externally set by an external divider circuit and an external variable capacitor. The power switch circuit selectively connects various circuit sections of the battery capacity measuring device to a power source, depending on the operating state, charging or discharging, of the secondary battery.