An electronic musical instrument, which can easily select waveform data assigned to each key or each key range of a keyboard, is provided. When assignment of waveform data to a key range including one or more keys of a keyboard is edited, the assignment state of the waveform data is displayed, and a mode setting operation of an operating unit is allowed in response to display of the assignment state of the waveform data. Waveform selection mode is set in response to operation of the operating unit by the user. When a key of the keyboard is operated in waveform selection mode, waveform data assigned to the operated key is selected, and an assignment state of the selected waveform data is allowed to be editable.