Abstract: Respecting plural accompaniment patterns belonging to a common accompaniment style, an order is predetermined in which accompaniment patterns are sequentially changed. For example, this order may be predetermined to be an order in which a change of the accompaniment patterns can accomplish a more natural change in an accompaniment tone. Data indicative of a performance state on a keyboard is compared with a predetermined reference value. Whenever a comparison condition is satisfied, change of the accompaniment patterns is effected in the predetermined order. Data related to a changed-over accompaniment pattern is read out from a memory, based on which data an automatic accompaniment tone is generated. There may be a plurality of the predetermined orders. One order may be such that the accompaniment patterns are changed to allow an automatic accompaniment tone to achieve a progressively flourishing mood and another order may be such that brings an effect opposite to that achieved by the one order.