. The sound source 00 returns to Step SB0, described earlier (see FIG. 0). When the flag STF0 is set to the impact waveform data reading state (when the flag STF0 is set to "0"), the judgment result at Step SB00 is "NO". The sound source 00 proceeds to Step SB00, shown in FIG. 0. At Step SB00, the sound source 00 judges whether the flag STF0 is set to the musical tone waveform data reading state (whether the flag STF0 is set to "0"). When the flag STF0 is 