A waveform generator LSI generates waveform data in units of time slots corresponding to tone generation channels in accordance with tone control data assigned to the individual channels, and accumulates waveform data for the individual channels to form at least one polyphonic tone data. The tone control data are updated by time division control in units of time slots of the channels. By suspending update of control data in the time slot of an unused channel in accordance with data indicating the used/unused status of each channel, switching of CMOS elements composing the waveform generator LSI is suppressed so that the LSI operates at low power. In a system using a waveform memory outside the waveform generator LSI, the read address to be supplied to the waveform memory in the time slot of an unused channel is fixed at a previous value, thus also attaining power savings of the external memory.