Respective sets of black keys and white keys of respective octaves of a keyboard 10 are defined as specific key range, respectively, to assign various tone colors of percussion instruments of a drum set to a plurality of keys included in the respective specific key ranges of the octaves. A specific key range has secondary key ranges to assign tone colors produced by different playing techniques of the same musical instrument. A depression of any key of a specific key range results in generation of a musical tone having a tone color of a percussion instrument assigned to the specific key range. To a pedal unit 20, a tone color of “bass drum” is assigned. Tone colors of “hi-hat” assigned to the keyboard 10 are controlled such that a depression of any key to which “hi-hat” is assigned with or without operation of the pedal unit 20 results in generation of a musical tone of open hi-hat or closed hi-hat.