The server switching controller system of the present invention includes a first server (2) and a second server (3) connected to a common controller (30, 20) installed in a vehicle (50) via communication means (14, 15, 8, 9, 10, and 11) to freely communicate with each other with said first server (2) and said second server (3) each having a server ID and an address (ID1 and ID2) for identifying itself; and with the controller (30, 20) having a controller ID and an address ID3 corresponding to the first server ID or an address ID4 corresponding to the second server ID, respectively such that the controller (30, 20) in the vehicle 50 will be connected either to first server (2) or to the second server (3) based on the address of the first server (2) or second server (3) respectively and program means for switching the address setting in the controller to permit the controller to selectively communicate with either the first or second server so as to operate either in a normal mode or in an overwrite mode.