PURPOSE: To select more clear chords on the musical instrument which can sound scales and to enable a more effective musical performance.

CONSTITUTION: When one of 19 operation elements provided for each octave is operated, its key code KC and a key-ON signal KON are outputted and inputted to a frequency number memory 14 storing frequency numbers F as many as the product of 19 and the number of octaves for each key code KC, and, a frequency number F is outputted as a phase address data ADD to a musical sound signal generating circuit 16. On the basis of this phase address data ADD, a musical sound signal generating circuit 16 outputs a musical sound waveform signal, which is inputted to a sound system 17 to generates a musical sound. Here, the frequency ratio of each musical sound, generated by operation of element KEYm (1≤m≤19) and KEYm+1, is 19√2.