The tone pitch of a given tone waveform is detected by forming an envelope waveform of the given tone waveform, holding the level of the envelope waveform at each of the zero cross times of the given tone waveform and releasing such holding starting new holding when the level of the given tone waveform exceeds the held level of the envelope waveform, and determining the pitch of the given tone waveform based on the period between the adjacent zero cross times, A correction target note pitch is provided, to which the detected tone pitch of the given tone waveform is corrected. The detected tone pitch, the correction target note pitch and the amount of correction are exhibited for the user to visually understand the pitch correction.