Method of and apparatus for automatically playing arpeggio in electronic musical instrument

An electronic musical instrument including key switches which are connected in a matrix of twelve note lines times six octave lines. The note lines are scanned cyclically at a high speed and the octave lines are detected one by one cyclically to determine the closed key switches. Everytime a closed key switch is detected, the scanning operation pauses for a predetermined period of time and a note indicating signal is delivered. The note indicating signal causes the production of a tone signal of that note for a predetermined octave. The number of the detection cycles is counted by a counter, and the detection of the same note in the next cycle causes the production of a tone signal of the same note for the next octave, the counter causing the shifting of the sounding octave. The octave shifting is repetitively carried out upward or downward or reciprocally within a range of certain octaves. Thus an automatic arpeggio performance is realized.