A first voltage source terminal, to which a first voltage is input, is connected to a maximum voltage terminal of serially-connected secondary batteries to be monitored. A second voltage source terminal, to which a second voltage is input, is connected to a minimum voltage terminal of the secondary batteries. A battery-voltage detecting unit outputs a detection signal based on a result of a voltage monitoring. A first reference-voltage generating unit receives the first and the second voltages as operating voltages, and generates a first reference voltage. A voltage converting unit receives the detection signal, and converts the detection signal received into either the first reference voltage or the second voltage. An output terminal outputs the detection signal converted, as an output detection signal.