A Plurality of key switches for tone-generating are arranged two-dimensionally. Mode setting section sets a tone adjusting mode in which the key switches are caused to function as tone-adjusting operators. In the tone adjusting mode, adjustment of a predetermined tone factor (e.g., tone pitch, tone length, tone volume or tone color) is permitted in response to operation of the key switch. For example, once a user moves a finger to change a Y-coordinate position of the key switch in the tone adjusting mode, an amount of the movement, i.e. a difference between Y-coordinates of two or more successively-operated key switches, is detected, and the thus-detected movement amount is set as a value for adjusting a tone volume or the like. All of light-emitting elements located at Y-coordinate positions of the key switches may be illuminated in a line, to allow the user to visually confirm the adjustment and operation.