In response to detection of a note-on instruction, a CPU assigns a tone generating unit comprising two tone generating channels and sets tone color control data of the assigned tone generating unit into tone generator registers. The tone color control data includes a parameter common to the two channels. Once the CPU gives a tone generation start instruction to a tone generator, the tone generator accumulates a frequency number common to the two channels to thereby generate a progressive phase common to the two channels. Waveform readout section reads out left-channel and right-channel waveform data from a waveform memory on the basis of the phase and waveform selecting information of the left and right channels. Tone characteristics of the read-out left- and right-channel waveform data are controlled by a characteristic control section on the basis of a characteristic control parameter common to the two channels.