A voltage-detecting circuit includes a flying capacitor; a first switch circuit allowing plural electric cells connected in series, so that polarity of voltage across electrodes of the flying capacitor charged by one of the electric cells is opposite to polarity of voltage across the electrodes of the flying capacitor charged by an adjacent one of the electric cells; a second switch circuit discharging the flying capacitor; an output circuit outputting a signal depending on the voltage across the flying capacitor; a shield arranged around the flying capacitor electrodes to substantially equalize parasitic capacitances between the shield and each of the electrodes; and a voltage-controlling circuit equalizing voltage between one of the electrodes of the flying capacitor and the shield when charging the flying capacitor, with voltage between another one of the electrodes of the flying capacitor and the shield when discharging the flying capacitor.