In a portable communication terminal that functions as a communication instrument by installing an identification recording medium having subscriber information recorded therein, an application acquiring unit 104 is operative to transmit a contract number recorded in the identification recording medium to the server when the identification recording medium is installed for the first time, and downloads an application program linked to the contract number from the server. A checking unit 108 is operative to check identification information embedded in the application program against identification information embedded in the identification recording medium. A function restricting unit 110 is operative to restrict the use of at least a part of the functions of the application program when the identification information of the application program does not match the identification information of the identification recording medium.