A data processing system with data transmission failure recovery measures includes a plurality of first POS terminals and a plurality of second POS terminals. Each POS terminal is connected to two transmission lines. A first file server is connected to one of the transmission lines. A second file server having stored contents identical to that of the first file server is connected to the other transmission line. The first POS terminal accesses the first file server, and the second POS terminal accesses the second file server during normal transmission. This permits incorporation of a plurality of files and allows a large number of POS terminals to be installed while alleviating access concentration of the files. Because the transmission lines and files are multiplexed, data processing including data transmission can be continued, thereby avoiding a system down, by switching from the normal transmission line or file when a transmission failure occurs. The two file servers are connected to each other via another transmission line to update the stored content of one file via the third transmission line to conform to the update of the stored contents of the other file. Thus, after updating, the stored contents of those files are always identical and the same data can always be obtained regardless of which file is accessed.