An external storage device stores automatic music playing data files, each file including data of a progression of musical notes constituting a performance of a music piece, and registration data files, each file including data of a set of parameters to determine the conditions for the performance of the music piece. While an automatic music playing data file of a piece of music and registration data files are loaded into a working memory and are being processed to play the current piece of music automatically, the next automatic music playing data file of the next piece of music to be played and the registration data files to be used next are prefetched from the external storage device into an internal storage device temporarily to be prepared for being transferred to the working memory for the successive automatic music playing after the automatic playing of the current music piece is over. Thus, dead time between the adjacent pieces of automatically played music and delay in effectuating the registrations will be avoided.