Program data stored in the recording medium of a general control apparatus coupled to a network is stored in the recording medium of a control apparatus as a rewritten subject of program data in the following manner. First, program data stored in a recording medium contained within the general control apparatus is sent via the network of a vehicle to the recording medium of a second control apparatus as the rewritten subject of program data (see a path L1). In this case, the program data 21 stored in the recording medium contained in the general control apparatus for generally controlling the control apparatuses is sent to the network of the vehicle when it is determined to be optimum by the CPU 12c of the general control apparatus. The program data sent to the network of the vehicle is sent via the network of the vehicle to the second control apparatus as the rewritten subject of program data. Then, the second control apparatus as the rewritten subject of program data stores the program data sent via the network of the vehicle into the recording medium.