Even with a large ripple voltage superposed on a voltage of a battery cell, the voltage of the battery cell can be measured accurately. In a battery monitoring device, a supply circuit, based on a reference voltage inputted from an assembled battery, generates a driving voltage for driving each of switching elements, of a selection circuit and supplies the driving voltage to the selection circuit. The reference voltage is inputted from the assembled battery to the supply circuit via a detecting filter circuit. As a result, a time constant of a route through which the reference voltage is inputted from the assembled battery to the supply circuit is approximately equal to time constants of detecting filter circuits.