A first microcomputer in an ECU outputs a CID of the ECU in response to a request from a scan tool when the ECU has multiple microcomputers implemented therein. Each of the multiple microcomputers has an additive value stored therein for counting an update of the software. The additive values from the multiple microcomputers are added as a sum total of the ECU that is further added to a CID base value. The sum total of the ECU added to the CID base value is then output as the CID of the ECU from the first microcomputer to the scan tool. Therefore, information stored in the first microcomputer is not necessarily changed for outputting an updated CID (e.g., software product number information) from the ECU.