A subscriber identity module (SIM) for subscriber identification configured so as to be detachably loaded on a mobile communication terminal device has a application section for storing an externally downloaded application program, a processing section (or a SAT function section) for executing this application program, a storage section for storing file administrative description, file description, and file data, and file administration section for administering these information and data. The processing section, after the downloading of the application program, executes the downloaded application program to control the file administration section. Consequently, access to the data stored in the subscriber identity module is prevented, thereby preventing the third party to access the data stored in the subscriber identity module of the lost or stolen mobile communication terminal.