Abstract: 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.