An automatic player piano has a feedback control loop for each of the black/white keys; the controller firstly determines a reference trajectory, i.e., a target key position varied with time for each key to be moved in the play-back, and calculates a target key velocity, and compares a true key position reported from a key sensor and a true key velocity calculated from the true key position with the target key position and target key velocity for optimizing the duty ratio of the driving signal; the positional difference and the velocity difference are independently multiplied by a positional gain and a velocity gain so as to determine the optimum duty ratio; since the ratio of the velocity gain to the positional gain is 1 to 3, the key travels along the reference trajectory without oscillation and overshoot.