An electronic musical instrument enables a phrase that is stored as audio waveform data to be played back at an arbitrary tempo. The instrument includes an operator that allows the performer to change the readout position of the waveform data manually, enabling the performer to increase, decrease or reverse the speed of waveform data playback temporarily. Upon ceasing use of the operator, the playback of the waveform data returns to synchronization with the previously set tempo at a readout position that would be the current readout position had the operator not been used by the performer.