A relay (20) receives a battery information acquisition time from each battery module (10) and calculates measurement time differential information Δt, that is, a time difference between the battery information acquisition time as a reference and the battery information acquisition time of another battery module (10) among the received battery information acquisition times, for each battery module (10). A measurement time correction unit (115) of each battery module (10) corrects a measurement time by the measurement time differential information Δt, using the measurement time differential information Δt received from the relay (20) to adjust the battery information acquisition time of each battery module (10) to the same time.