An automatic player piano is equipped with an electronic supporting system, which makes a player learn an optimum pedal stroke to a half pedal region; while the player is practicing a music tune on the piano, the electronic supporting system monitors the damper pedal; when the player starts to depress the damper pedal, the electronic supporting system exerts an assisting force on the damper pedal so as to make the player feel the damper pedal light; when the damper pedal reaches an entrance of the half pedal region, the electronic supporting system removes the assisting force from the damper pedal so that the player feels the damper pedal heavy, whereby the player learns the pedal stroke to the half pedal region through the change of load borne by the player.