A battery monitor circuit includes a first monitoring unit for detecting voltages of battery cells in a first group, a second monitoring unit for detecting voltages of battery cells in a second group, and a current cancellation unit for canceling a difference between first and second currents that flow through the first and second monitoring units, respectively. One terminal of a series connection of the battery cells in the first and second groups and one terminal of the first monitoring unit are connected, the other terminal of the first monitoring unit and one terminal of the second monitoring unit are connected, and the other terminal of the second monitoring unit and the other terminal of the series connection are connected. The current cancellation unit is disposed between a connection point between the first and second monitoring units and a middle connection point in the middle of the series connection.