An ECU compares a plurality of pieces of data that include the same identification information if they are received within a preset time range. If it is determined, as a result of the comparison, that there are one or more data groups each consisting of data having the same content, and the number of largest data groups with the largest number of pieces of data among the one or more data groups is one, the ECU selects data included in the largest data group as proper data. In the ECU, if it is determined that, as a result of comparison, that there is no data group, or the number of largest data groups is greater than one, the contents of the plurality of pieces of data received within the time range are ignored.