When anomalous vehicle actions occur in a vehicle multiple times, it is determined whether each action data is included in a series of action data sets that are closely related mutually or an irrelevant independent action data set. When it is included in the series of action data sets, the ECUs record the series of action data sets in respective own memories according to a predetermined recording order. In contrast, when it is included in the independent action data set, an earliest ECU that is earliest in the recording order records the action data by overwriting its own memory. In this case, the earliest ECU transmits an instruction to other ECUs to delete all past action data that are recorded in own memories of the other ECUs.