Abstract: For easy adjustment of a key driver assembly, there is disclosed an automatic music player system having at least a recording mode and a reproducing mode and comprising (a) a piano having a keyboard provided with a plurality of keys, a sound generator mechanism operative to mechanically generate sounds when the keys are actuated, and an effector mechanism operative to affect the sound generated by the sound generator mechanism upon actuation, (b) a control unit located at the outside of the piano and operative to store a musical information produced by a keying-in on the keyboard and an operation of the effector mechanism in the recording mode and to produce drive signals based on the musical information stored therein in the reproducing mode, (c) a key driver assembly provided with a plurality of actuators corresponding to the keys, respectively, and responsive to the drive signal for selectively actuating the keys, (d) an effector driver assembly responsive to the drive signal and operative to actuate the e