A communication network (3020) is a bus type communication network that communicably connects each battery module (2000). In the battery module (2000), a communication identifier that is used in communication through the communication network (3020) is set. A transmission unit (2020) transmits identifier information to all of the other battery modules (2000) through the communication network (3020). The identifier information indicates a candidate identifier that is a candidate of the communication identifier. A communication arbitration unit (2060) performs communication arbitration for the identifier information transmitted by the transmission unit (2020). In a case of winning in the communication arbitration, a decision unit (2080) decides the candidate identifier indicated in the transmitted identifier information as the communication identifier used by the battery module (2000). On the other hand, in a case of losing in the communication arbitration, the transmission unit (2020) transmits the identifier information again.