In the system of the invention, a music playing data file is extracted from a given musical work resource such as an electronic music score data file, a printed sheet of music and an audio signals of a musical performance, to be utilized for playing music automatically by means of a tone generator device. The extracted music playing data file is encrypted using an encryption key to be stored in a storage device or to be transmitted to an automatic music playing apparatus. The stored or the transmitted music playing data file is decrypted beforehand to be used for automatic music playing. After the decrypted music playing data file has been utilized, the decrypted music playing data file is deleted from the system so that no unencrypted data file remains in the system.