A silent piano is available for a performance through electronic tones, and a player can give a timbre different from that of an acoustic piano to the electronic tones; when the player specifies a timbre of another acoustic musical instrument having a compass narrower than the compass of the acoustic piano, the key levers outside of the compass are never depressed in the performance, and several musical performance styles such as mute, glissando, tremolo and so fourth are assigned to the idle key levers; while the player is fingering on the keyboard, the player depresses one of the idle key levers and, thereafter, the black and white key levers in the compass, then, the electronic tones are produced in the selected musical performance style; the idle key levers are not mixed in the compass so that the player is less liable to be mistakenly depress the idle key levers.