synchronize with zero cross points indicated by symbols 1811 1813 of a prescribed phase in this example the data value changes from negative to positive of audio data 1810 in this example a waveform 1821 between a key push indicated by symbol 1811 at first regular key push timing and a key push indicated by symbol 1812 at the next regular key push timing is delimited by zero cross points having the same phase likewise a waveform 1822 between the next pair of key pushes indicated by symbols 1812 and 1813 at the corresponding pieces of regular key push timing is delimited by zero cross points having the same phase although in the embodiment each piece of regular key push timing is set so as to synchronize with a zero cross point of a prescribed phase of audio data the invention is not limited to such a case in the example of fig1 a player makes a first key push indicated by symbol 1911 earlier than the regular timing in this case a zero cross point indicated by symbol 1931 that is closest to the key push timing of the player on its future side in time series is found in the audio data and a waveform 1941 between the key push indicated by symbol 1811 in fig1 at the first regular key push timing and the key push indicated by symbol 1812 in fig1 at the next regular key push timing is connected to the waveform before the thus found zero cross point in fig1 the waveform 1941 between the two pieces of.