Abstract: Tone forming channels generate tone signals corresponding to tone pitch information assigned thereto with characteristics responsive to tone element control signals supplied thereto. An assignment order setting section selects desired channels and establishes an order of assignment of the selected channels. An assignment section sequentially changes, at each timing of generation of a tone, a channel to which a tone to be generated should be assigned in accordance with the established assignment order. In the channels whose assignment order has been established, tones whose tonal quality are different from one another are formed. A group setting section divides the tone forming channels into plural groups. The assignment section performs, group by group, assignment of a tone to be generated to any of channels in each group. Tones of different tonal quality are formed between different groups.