In a musical sound waveform synthesizer apparatus, a performance event information receiver receives performance event information representing musical performance events which successively occur as a musical performance progresses. A musical sound synthesizer synthesizes a waveform of a musical sound corresponding to each musical performance event based on the performance event information. An overlap detector detects whether or not a first musical sound and a second musical sound overlap with each other based on the performance information. A sound length meter obtains a sound length of thefirst musical sound based on the received performance event information. When the first musical sound and the second musical sound overlap with each other, the musical sound synthesizer instantly terminates synthesizing of a waveform of the first musical sound and starts synthesizing of a waveform of the second musical sound if the sound length of the first musical sound does not exceed a predetermined sound length.