An electronic musical instrument includes a sound source LSI to generate a musical sound using a RAM that retains waveform data that has been selectively read from a plurality of waveforms stored in a large-capacity flash memory, and smoothly executes transfer of additional waveform data from the flash memory to the RAM when the requisite waveform data is not retained in the RAM during the performance. Performance data is generated by a sequencer, a prescribed delay time is applied to the performance data by an event time generator and an event delay buffer so as to provide for sufficient time for the transfer of the additional waveform if such transfer is needed. A musical sound is generated by an event buffer and a sound source driver on the basis of the delayed performance data.