A single unified server transmits/receives information in a common interface format with respect to a plurality of service servers and a portable terminal and has a common database in a data format corresponding to the common interface format, and the plurality of service servers connects to clients in a specific interface format to provide services by individual applications, respectively, and coverts a data format between higher-rank data transmitted/received in the common interface format and lower-rank data transmitted/received in the specific interface format. The portable terminal transmits/receives information in the common interface format using the application.