The copyright or the use right is sometimes prescribed in a sound source data file used as BGM, so that, in a sound source data file, acquired by a user, copying and re-distribution need to be suppressed without detracting from its serviceability. To this end, a VoIP client writes a downloaded sound source data file in a prescribed folder in a HDD forming an external storage device. When the writing is finished regularly, a hash value in the folder is calculated. The so calculated hash value is set in the user-oriented system information in the external storage device. When the VoIP client is booted for VoIP call, a hash value in a prescribed folder in the external storage device is calculated, and the so calculated hash value is compared to the hash value stored as the system information. If the result of comparison indicates that the hash value calculated is equal to the hash value stored, the sound source data file, stored in the prescribed area in the external storage device, is displayed on the GUI.