notes which are to be sounded with respect to the root note of the chord also the chord timing signal cdt and the bass timing signal bst are arranged to instruct the timings of their sounding which usually do not coincide with each other a bass note key code forming circuit 28 is designed to form key code data representing the bass notes which are to be sounded in accordance with the chord name data cnd and the bass note decisive data bsp in case the mode signal abc is 34 1 34 the bass note key code data thus formed are delivered out along with the data category signal bs 34 1 34 at a predetermined timing for each completion of one scanning cycle of the key coder 20 it should be noted here that the data category signal bs indicates that the delivered out key code data represent the bass note key code data a tone color selector 30 contains on the panel surface of the body of the musical instrument a number of tone color selection manipulation knobs which are provided for various categories of musical tones respectively such as for melody chord bass and so forth a selected tone color detection and tone color data generation circuit 32 is arranged to detect by scanning the tone color selected in the tone color selector 30 and to generate tone color data for respective categories of tones a channel assignment controlling circuit 34 has a ring counter 36 which generates sequential pulses p 1 u02dc p 5 in correspondence to the first to fifth channel.