The present invention aims to downsize a configuration for achieving confidentiality of data on an air link of a mobile terminal and/or data for communication with a partner terminal. A mobile terminal 1 communicating with plural base stations 4 and 1004 for providing plural different mobile communication networks/services achieves confidentiality of data on plural air links among the plural base stations 4 and 1004 using a single encrypting/decrypting unit 3.