A waveform memory WM stores fast decay waveform data representative of fast decay waveforms of different levels of strength and slow decay waveform data representative of a slow decay waveform of a strong strength. A CPU 21 controls a tone generator 15 to select at least a waveform data according to the level of strength of a touch from among the plurality of fast decay waveform data to read out the selected waveform data from the top address of the waveform data. In addition, the CPU 21 also controls the tone generator 15 to read out the slow decay waveform data, starting at an address placed further away from the top of the slow decay waveform data as the level of strength of the touch decreases. The read fast decay waveform data and the read slow decay waveform data is mixed together to be output.