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 1, a supply circuit 13, based on a reference voltage 17 inputted from an assembled battery 2, generates a driving voltage 18 for driving each of switching elements 110p, 111p, 111m, and 112m of a selection circuit 11 and supplies the driving voltage 18 to the selection circuit 11. The reference voltage 17 is inputted from the assembled battery 2 to the supply circuit 13 via a detecting filter circuit 120. As a result, a time constant of a route through which the reference voltage 17 is inputted from the assembled battery 2 to the supply circuit 13 is approximately equal to time constants of detecting filter circuits 120 to 122.