One state detector detects an abnormal state or a normal state relating to charge and discharge of a battery cell group in one battery module, and generates one detection signal representing the detected state. Another state detector detects an abnormal state or a normal state relating to charge and discharge of another battery cell group in another battery module, and generates another detection signal representing the detected state. One operation processing device sends the one detection signal generated by the one state detector to an external object. Another operation processing device sends the other detection signal generated by the other state detector to the external object. The one detection signal generated by the one state detector is transmitted to at least one of the other operation processing device and the other state detector via a signal line.