In an ECU reprogram data DB of a center device, data of an update program for a target ECU for a program update among a plurality of EUCs mounted in a vehicle is stored. In a configuration information DB, an “ECU ID” corresponding to each ECU and vehicle-related information such as an “ECU SW ID” for each application program stored in the ECU are stored along with the vehicle type. An ECU metadata database stores update data-related information pertaining to update data and attributes of the rewrite target ECU. A specification data generation unit generates specification data, based on the information stored in the configuration information database and the information stored in the ECU metadata database, to be transmitted to the vehicle together with update data to be written in the target ECU such that the data includes information related to the type, attributes, and update data for the target ECU and information indicative of a rewrite environment related to the data update.