An electronic musical instrument includes a plurality of keys respectively specifying different pitches when operated; a memory; and a sound processor. In response to a current operation of a current key, which is one of the plurality of keys, the sound processor retrieves the information stored in the memory for a previous operation, if any, of a previous key, which is a same as the current key or is another one of the plurality of keys, and performs a prescribed processing on a beginning part of the waveform data generated for the current operation of the current key in accordance with the retrieved information stored in the memory for the previous operation of the previous key so as to generate processed waveform data in response to the current operation of the current key. The resulting processed waveform data can be configured to better mimic artists' performance of an original instrument.