PURPOSE: To generate musical sound with diverse timbre by increasing and decreasing a set level for clipping an input sound signal within the half cycle of the input sound signal and distorting the input sound signal.

CONSTITUTION: A 1st output waveform selection processing circuit 500 compares an input waveform W(INP) and a plus-side threshold value W(TH0) and selects the input waveform W(INP) or plus-side threshold value W(TH0) as a plus-side output waveform W(OUT1). A 1st threshold value variation processing circuit 600 increases and decreases the plus-side threshold value W(TH0) by adding a plus-side rate value W(RAT0) and a 1st threshold comparison processing circuit 700 compares the result with a plus-side level value W(LVL0). A 1st threshold level rate read processing circuit 800 sets a new plus-side level value W(LV0) and a plus-side rate value W(RAT0). The minus side is similarly processed to determine a final output waveform W(OUT).