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 21 stored in a recording medium 12b contained within the general control apparatus 12 is sent via the network 15 of a vehicle to the recording medium 13a of a second control apparatus 13 as the rewritten subject of program data (see a path L1). In this case, the program data 21 stored in the recording medium 12b contained in the general control apparatus 12 for generally controlling the control apparatuses 13, 14 is sent to the network 15 of the vehicle when it is determined to be optimum by the CPU 12c of the general control apparatus 12. The program data sent to the network 15 of the vehicle is sent via the network 15 of the vehicle to the second control apparatus 13 as the rewritten subject of program data. Then, the second control apparatus 13 as the rewritten subject of program data stores the program data 21 sent via the network 15 of the vehicle into the recording medium 13a.