Automatic accompaniment apparatus for electronic musical instrument

In an automatic accompaniment apparatus for electronic musical instrument capable of automatically generating accompaniment tones such as base tones, chord tones and arpeggio tones, arrangement is provided so that, at each time of depressing keys on an accompaniment keyboard, accompaniment key data for accompaniment tones which may possibly be sounded, are previously formed and secured, and the selected ones of the key data for the selected accompaniment are outputted at accompaniment tone generating timings synchronous with the rhythm. Thus bass tone, chord tones, arpeggio tones etc. may be generated in sufficient synchronous relation with a selected rhythm even by adopting a time-divisional processing using a low-speed compact computer such as a micro-computer.