A connection setting part holds a selecting condition for a binding to use; a common interface part receives a connection request from a common interface execution code to be executed by a client; a reading/analyzing part obtains the selecting condition from the connection setting part; an environment information obtaining part obtains environment information of the client and/or a server; a connection selecting determination part determines the binding to use based on the selecting condition and the environment information; and a calling part carries out connection to the Web service with the execution code corresponding to the determined binding.